diff --git a/Makefile b/Makefile
index 6c45e46..e46d43a 100644
--- a/Makefile
+++ b/Makefile
@@ -4,11 +4,10 @@ pwd = $(shell pwd)
 .PHONY: all test clean realclean
 
 all:
-	mkdir -p bin
-	go build -o bin/sigtool .
+	./build -s
 
 test:
 	go test ./sign
 
 clean realclean:
-	rm -f bin/sigtool
+	rm -rf bin
diff --git a/README.md b/README.md
index f8a0fa3..5921fef 100644
--- a/README.md
+++ b/README.md
@@ -4,15 +4,54 @@
 
 
 ## What is this?
-`sigtool` is an opinionated tool to generate, sign and verify Ed25519
-signatures on files.  In many ways, it is like like OpenBSD's signify_
--- except written in Golang and definitely easier to use.
+`sigtool` is an opinionated tool to generate keys, sign, verify, encrypt &
+decrypt files using Ed25519 signature scheme.  In many ways, it is like
+like OpenBSD's [signify][1] -- except written in Golang and definitely
+easier to use.
 
 It can sign and verify very large files - it prehashes the files
-with SHA-512 and then signs the SHA-512 checksum.
+with SHA-512 and then signs the SHA-512 checksum. The keys and signatures
+are YAML files and so, human readable.
 
-All the artifacts produced by this tool are standard YAML files -
-thus, human readable.
+It can encrypt & decrypt files by converting the Ed25519 keys to their
+corresponding Curve25519 variants. This elliptic co-ordinate transform
+follows [FiloSottile's writeup][2]. The file encryption uses
+AES-GCM-256 (AEAD); the input is broken into chunks and each chunk is
+AEAD encrypted. The default chunk size is 4MB (4 * 1048576 bytes). 
+
+A random 32-byte key is used to actually encrypt the file contents in
+AES-GCM mode. This file-encryption key is **wrapped** using the recipient's
+public key. Thus, a given input file (or stream) can be encrypted to be
+read by multiple recipients - each of whom is identified by their Ed25519
+public keys. The file-encryptionb-key can optionally be wrapped using the
+sender's Private Key - this authenticates the sender. If this private key is
+not provided for the encrypt operation, then `sigtool` generates ephemeral
+Curve25519 keys and wraps the file-encryption key using the ephemeral 
+private key and the recipient's public key.
+
+Every encrypted file starts with a header:
+
+    7 byte magic ("SigTool")
+    1 byte version number
+    4 byte header length
+    32 byte SHA256 of the encryption-header
+
+The encryption-header is described as a protobuf file (sign/hdr.proto):
+
+```protobuf
+    message header {
+        uint32 chunk_size = 1;
+        bytes  salt = 2;
+        repeated wrapped_key keys = 3;
+    }
+
+    message wrapped_key {
+        bytes pk_hash = 1; // hash of Ed25519 PK
+        bytes pk = 2;       // curve25519 PK
+        bytes nonce = 3;    // AEAD nonce
+        bytes key = 4;      // AEAD encrypted key
+    }
+```
 
 ## How do I build it?
 With Go 1.5 and later:
@@ -21,7 +60,9 @@ With Go 1.5 and later:
     cd sigtool
     make
 
-The binary will be in `./sigtool`.
+The binary will be in `./bin/$HOSTOS-$ARCH/sigtool`.
+where `$HOSTOS` is the host OS where you are building (e.g., openbsd)
+and `$ARCH` is the CPU architecture (e.g., amd64).
 
 ## How do I use it?
 Broadly, the tool can:
@@ -29,6 +70,8 @@ Broadly, the tool can:
 - generate new key pairs (public key and private key)
 - sign a file
 - verify a file against its signature
+- encrypt a file
+- decrypt a file
 
 ### Generate Key pair
 To start with, you generate a new key pair (a public key used for
@@ -73,6 +116,22 @@ e.g., to verify the signature of *archive.tar.gz* against
 
     sigtool verify /tmp/testkey.pub archive.sig archive.tar.gz
 
+### Encrypt a file by authenticating the sender
+If the sender wishes to prove to the recipient that they  encrypted
+a file:
+
+   sigtool encrypt -s mykey.key theirkey.pub -o archive.tar.gz.enc archive.tar.gz
+
+
+This will create an encrypted file *archive.tar.gz.enc* such that the
+recipient in possession of *theikey.key* can decrypt it. Furthermore, if
+the recipient has *mykey.pub*, they can verify that the sender is indeed
+who they expect.
+
+### Encrypt a file *without* authenticating the sender
+
+### Decrypt a file
+
 ## How is the private key protected?
 The Ed25519 private key is encrypted using a key derived from the
 user supplied pass phrase. This pass phrase is used to derive an
@@ -111,6 +170,8 @@ A serialized Ed25519 public key looks like so:
 ### Ed25519 Private Key
 And, a serialized Ed25519 private key looks like so:
 
+```yaml
+
     esk: t3vfqHbgUiA733KKPymFjWT8DdnBEkiMfsDHolPUdQWpvVn/F1Z4J6KYV3M5rGO9xgKxh5RAmqt+6LKgOiJAMQ==
     salt: pPHKG55UJYtJ5wU0G9hBvNQJ0DvT0a7T4Fmj4aPB84s=
     algo: scrypt-sha256
@@ -118,6 +179,7 @@ And, a serialized Ed25519 private key looks like so:
     Z: 131072
     r: 16
     p: 1
+```
 
 The Ed25519 private key is encrypted using Scrypt password hashing
 mechanism. A user supplied passphrase to protect the private key
@@ -146,9 +208,12 @@ ensures that the supplied passphrase yields the same value as
 ### Ed25519 Signature
 A generated signature looks like below after serialization:
 
+```yaml
+
     comment: inpfile=/tmp/file.txt
     pkhash: 36z9tCwTIVNwwDlExrB0SQ==
     signature: ow2oBP+buDbEvlNakOrsxgB5Yc/7PYyPVZCkfyu7oahw8BakF4Qf32uswPaKGZ8RVz4uXboYHdZtfrEjCgP/Cg==
+```
 
 Here, ```pkhash`` is a SHA256 of the public key needed to verify
 this signature.
@@ -163,4 +228,5 @@ See the file ``LICENSE.md`` for the full terms of the license.
 ## Author
 Sudhi Herle <sw@herle.net>
 
-.. _signify: https://www.openbsd.org/papers/bsdcan-signify.html
+[1]: https://www.openbsd.org/papers/bsdcan-signify.html
+[2]: https://blog.filippo.io/using-ed25519-keys-for-encryption/
diff --git a/build b/build
new file mode 100755
index 0000000..8869d0a
--- /dev/null
+++ b/build
@@ -0,0 +1,373 @@
+#! /usr/bin/env bash
+
+# Tool to build go programs in this repo
+#
+# - it tacks on a version number for use by the individual tools
+# - it supports git and mercurial version#
+# 
+# NB:
+#   o the attempt at decoding dirty repo state for mercurial is
+#     borked. It doesn't know about untracked files
+#
+# (c) 2016 Sudhi Herle
+#
+# License: GPLv2
+#
+Progs=".:sigtool"
+
+# Relative path to protobuf sources
+# e.g. src/foo/a.proto
+Protobufs="sign/hdr.proto"
+
+
+# -- DO NOT CHANGE ANYTHING AFTER THIS --
+
+Z=`basename $0`
+PWD=`pwd`
+
+Static=0
+Dryrun=0
+Prodver=0.1
+Verbose=0
+
+hostos=$(go env GOHOSTOS)       || exit 1
+hostcpu=$(go env GOHOSTARCH)    || exit 1
+
+[ -f ./version ] && Prodver=$(cat ./version)
+
+die() {
+    echo "$Z: $@" 1>&2
+    exit 0
+}
+
+warn() {
+    echo "$Z: $@" 1>&2
+}
+
+case $BASH_VERSION in
+    4.*|5.*) ;;
+
+    *) die "I need bash 4.x to run!"
+        ;;
+esac
+
+
+# build a tool that runs on the host - if needed.
+hosttool() {
+    local tool=$1
+    local bindir=$2
+    local src=$3
+
+    local p=$(type -P $tool)
+    if [ -n "$p" ]; then
+        echo $p
+        return 0
+    fi
+
+    # from here - we want this dir to find all build artifacts
+    PATH=$PATH:$bindir
+    export PATH
+
+    p=$bindir/$tool
+    if [ -x $p ]; then
+        echo $p
+        return 0
+    fi
+
+    # build it and stash it in the hostdir
+    echo "Building tool $tool from $src .."
+    $e go get -d      $src || exit 1
+    $e go build -o $p $src || exit 1
+    echo $p
+    return 0
+}
+
+
+usage() {
+
+    cat <<EOF
+$0 - A Go production build tool that adds git-repository information,
+product version, build-timestamp etc. It supports cross-compilation,
+static linking and generating protobuf output.
+
+If needed, it uses the gogo-slick protobuf compiler [github.com/gogo/protobuf].
+
+Build output is in bin/\$OS-\$CPU for a given OS, CPU combination.
+
+Usage: $0
+       $0 [options] [PROGS]
+
+Where OS-ARCH denotes one of the valid OS, ARCH combinations supported by 'go'.
+And, PROGS is one or more go programs.
+
+With no arguments, $0 builds: $Progs (source in ./src/)
+
+If ./version is present, its content are used as version number for the binary.
+
+Options:
+    -h, --help          Show this help message and quit
+    -s, --static        Build a statically linked binary [False]
+    -V N, --version=N   Use 'N' as the product version string [$Prodver]
+    -a X, --arch=X      Cross compile for OS-CPU 'X' [$hostos-$hostcpu]
+    -n, --dry-run       Dry-run, don't actually build anything [False]
+    -t, --test          Run "go test" on modules named on the command line [False]
+    -v, --verbose       Build verbosely (adds "-v" to go tooling) [False]
+    --vet               Run "go vet" on modules named on the command line [False]
+    -x                  Run in debug/trace mode [False]
+EOF
+
+    exit 0
+}
+
+host=`uname|tr '[A-Z]' '[a-z]'`
+export GO15VENDOREXPERIMENT=1
+
+declare -A oses
+declare -A cpus
+declare -A cgo
+
+# Supported & Verified OS/CPU combos for this script
+oslist="linux android openbsd freebsd darwin dragonfly netbsd windows"
+needcgo="android"
+cpulist="i386 amd64 arm arm64"
+cpualias_i386="i486 i586 i686"
+cpualias_amd64="x86_64"
+cpualias_arm64="aarch64"
+
+# CGO Cross-Compilers for various CPU+OS combinations of Android
+android_i386=i686-linux-android-gcc
+android_arm64=aarch64-linux-android-gcc
+android_arm=arm-linux-androideabi-gcc
+
+# initialize the various hash tables
+for o in $oslist;  do oses[$o]=$o; done
+for o in $needcgo; do cgo[$o]=$o;  done
+for c in $cpulist; do
+    cpus[$c]=$c
+    a="cpualias_$c"
+    a=${!a}
+    for x in $a; do cpus[$x]=$c; done
+done
+
+
+Tool=
+doinit=0
+args=
+
+#set -x
+ac_prev=
+for ac_option
+do
+  shift
+
+  if [ -n "$ac_prev" ]; then
+    eval "$ac_prev=\$ac_option"
+    ac_prev=
+    continue
+  fi
+
+  case "$ac_option" in
+      -*=*) ac_optarg=`echo "$ac_option" | sed 's/[-_a-zA-Z0-9]*=//'` ;;
+      *) ac_optarg= ;;
+  esac
+
+
+  case "$ac_option" in
+        --help|-h|--hel|--he|--h)
+            usage;
+            ;;
+
+        --arch=*)
+            Arch=$ac_optarg
+            ;;
+        -a|--arch)
+            ac_prev=Arch
+            ;;
+
+        --version=*)
+            Prodver=$ac_optarg
+            ;;
+        --test|-t)
+            Tool=test
+            ;;
+
+        --vet)
+            Tool=vet
+            ;;
+
+        -V|--version)
+            ac_prev=Prodver
+            ;;
+        -v|--verbose)
+            Verbose=1
+            ;;
+
+        -s|--static)
+            Static=1
+            ;;
+
+        --dry-run|-n)
+            Dryrun=1
+            ;;
+
+        --debug|-x)
+            set -x
+            ;;
+
+        *) # first non option terminates option processing.
+           # we gather all remaining args and bundle them up.
+            args="$args $ac_option"
+            for xx
+            do
+                args="$args $xx"
+            done
+            break
+            ;;
+  esac
+done
+[ $Dryrun  -gt 0 ] && e=echo
+
+# let every error abort
+set -e
+
+# This fragment can't be in a function - since it exports several vars
+if [ -n "$Arch" ]; then
+    ox=${Arch%%-*}
+    cx=${Arch##*-}
+    [ "$ox" = "$cx" ] && cx=$hostcpu
+
+    os=${oses[$ox]}
+    cpu=${cpus[$cx]}
+    [ -z "$os" ]  && die "Don't know anything about OS $ox"
+    [ -z "$cpu" ] && die "Don't know anything about CPU $cx"
+
+    export GOOS=$os GOARCH=$cpu
+    cross=$os-$cpu
+
+else
+    os=$hostos
+    cpu=$hostcpu
+    cross=$os-$cpu
+fi
+
+# If we don't need CGO, then we can attempt a static link
+if [ -n "${cgo[$os]}" ]; then
+    export CGO_ENABLED=1
+
+    # See if we have a specific cross-compiler for this CPU+OS combo
+    xcc="${GOOS}_${GOARCH}"
+    xcc=${!xcc}
+    if [ -n "$xcc" ]; then
+        p=`type -p $xcc`
+        [ -n "$p" ] || die "Can't find $xcc! Do you have compilers for $GOARCH available in PATH?"
+        export CC=$xcc
+    else
+        echo "$Z: No Cross compiler defined for $GOOS-$GOARCH. Build may fail.." 1>&2
+    fi
+else
+    if [ $Static -gt 0 ]; then
+        export CGO_ENABLED=0
+
+        isuffix="--installsuffix cgo"
+        ldflags="-s"
+        msg="statically linked"
+    fi
+fi
+
+# This is where build outputs go
+Bindir=$PWD/bin/$cross
+Hostbindir=$PWD/bin/$hostos-$hostcpu
+
+[ -d $Bindir ]     || mkdir -p $Bindir
+[ -d $Hostbindir ] || mkdir -p $Hostbindir
+
+# Get git/hg version info for the build
+if [ -d "./.hg" ]; then
+    xrev=$(hg id --id) || exit 1
+    brev=${xrev%+}
+    if [ "$brev" != "$xrev" ]; then
+        rev="hg:${brev}-dirty"
+    else
+        rev="hg:${brev}"
+    fi
+elif [ -d "./.git" ]; then
+    xrev=$(git describe --always --dirty --long --abbrev=12) || exit 1
+    rev="git:$xrev"
+else
+    rev="UNKNOWN-VER"
+    echo "$0: Can't find version info" 1>&2
+fi
+
+# Do Protobufs if needed
+if [ -n "$Protobufs" ]; then
+    slick=$Hostbindir/protoc-gen-gogoslick
+    slicksrc=github.com/gogo/protobuf/protoc-gen-gogoslick
+    pc=$(type -p protoc)
+
+    [ -z "$pc" ] && die "Need 'protoc' for building .."
+
+    slick=$(hosttool protoc-gen-gogoslick $Hostbindir $slicksrc) || exit 1
+    #if [ ! -f $slick ]; then
+    #   echo "Building $slick .."
+    #   $e go build -o $slick github.com/gogo/protobuf/protoc-gen-gogoslick || exit 1
+    #i
+
+    PATH=$Hostbindir:$PATH
+    export PATH
+
+    for f in $Protobufs; do
+        dn=$(dirname $f)
+        bn=$(basename $f .proto)
+        of=$dn/${bn}.pb.go
+        if [ $f -nt $of ]; then
+            echo "gogoslick: $f -> $of ..."
+            $e $pc --gogoslick_out=. $f || exit 1
+            $e gofmt -w $of
+        fi
+    done
+fi
+
+repover="main.RepoVersion=$rev"
+prodver="main.ProductVersion=$Prodver"
+date="main.Buildtime=`date -u '+%Y-%m-%dT%H:%M.%SZ'`"
+ldflags="-ldflags \"-X $repover -X $prodver -X $date $ldflags\""
+vflag=""
+
+[ $Verbose -gt 0 ] && vflag="-v"
+
+case $Tool in
+    test)
+        set -- $args
+        $e go test $vflag "$@"
+        ;;
+
+    vet)
+        set -- $args
+        $e go vet $vflag "$@"
+        ;;
+
+    *) # Default is to build programs
+        set -- $args
+        if [ -z "$1" ]; then
+            all=$Progs
+        else
+            all="$@"
+        fi
+
+        echo "Building $rev, $cross $msg .."
+
+        for p in $all; do 
+            if echo $p | grep -q ':' ; then
+                out=${p##*:}
+                dir=${p%%:*}
+            else
+                out=$p
+                dir=$p
+            fi
+            echo "   $dir: $out .. "
+            $e eval go build $vflag -o $Bindir/$out $isuffix "$ldflags" ./$dir || exit 1
+        done
+        ;;
+esac
+
+# vim: ft=sh:expandtab:ts=4:sw=4:tw=84:
diff --git a/crypt.go b/crypt.go
index 3bd6846..a12612a 100644
--- a/crypt.go
+++ b/crypt.go
@@ -18,8 +18,8 @@ import (
 	"io"
 	"os"
 
-	flag "github.com/opencoff/pflag"
 	"github.com/opencoff/go-utils"
+	flag "github.com/opencoff/pflag"
 	"github.com/opencoff/sigtool/sign"
 )
 
@@ -108,7 +108,10 @@ func encrypt(args []string) {
 		outfd = outf
 	}
 
-	var recip []*sign.PublicKey
+	en, err := sign.NewEncryptor(sk)
+	if err != nil {
+		die("%s", err)
+	}
 
 	for i := 0; i < len(args)-1; i++ {
 		fn := args[i]
@@ -116,11 +119,18 @@ func encrypt(args []string) {
 		if err != nil {
 			die("%s", err)
 		}
-		recip = append(recip, pk)
+
+		err = en.AddRecipient(pk)
+		if err != nil {
+			die("%s", err)
+		}
 	}
 
-	encryptFile(sk, recip, infd, outfd)
 
+	err = en.Encrypt(infd, outfd)
+	if err != nil {
+		die("%s", err)
+	}
 }
 
 // sigtool decrypt a.key [file] [-o output]
@@ -132,11 +142,13 @@ func decrypt(args []string) {
 
 	var envpw string
 	var outfile string
+	var pubkey string
 	var pw bool
 
 	fs.StringVarP(&outfile, "outfile", "o", "", "Write the output to file `F`")
 	fs.BoolVarP(&pw, "password", "p", false, "Ask for passphrase to decrypt the private key")
 	fs.StringVarP(&envpw, "env-password", "", "", "Use passphrase from environment variable `E`")
+	fs.StringVarP(&pubkey, "verify-sender", "v", "", "Verify that the sender matches public key in `F`")
 
 	err := fs.Parse(args)
 	if err != nil {
@@ -153,7 +165,6 @@ func decrypt(args []string) {
 	var inf *os.File
 	var pws, infile string
 
-
 	if len(envpw) > 0 {
 		pws = os.Getenv(envpw)
 	} else if pw {
@@ -169,6 +180,15 @@ func decrypt(args []string) {
 		die("%s", err)
 	}
 
+	var pk *sign.PublicKey
+
+	if len(pubkey) > 0 {
+		pk, err = sign.ReadPublicKey(pubkey)
+		if err != nil {
+			die("%s", err)
+		}
+	}
+
 	if len(args) > 1 {
 		infile = args[1]
 		if infile != "-" {
@@ -200,14 +220,21 @@ func decrypt(args []string) {
 		outfd = outf
 	}
 
-	decryptFile(sk, infd, outfd)
-}
 
+	d, err := sign.NewDecryptor(infd, pk)
+	if err != nil {
+		die("%s", err)
+	}
 
-func encryptFile(sk *sign.PrivateKey, pks []*sign.PublicKey, infd  io.Reader, outfd io.Writer) {
-}
+	err = d.SetPrivateKey(sk)
+	if err != nil {
+		die("%s", err)
+	}
 
-func decryptFile(sk *sign.PrivateKey, infd io.Reader, outfd io.Writer) {
+	err = d.Decrypt(outfd)
+	if err != nil {
+		die("%s", err)
+	}
 }
 
 
diff --git a/go.mod b/go.mod
index c43f3a4..ef96194 100644
--- a/go.mod
+++ b/go.mod
@@ -3,6 +3,7 @@ module github.com/opencoff/sigtool
 go 1.13
 
 require (
+	github.com/gogo/protobuf v1.3.1
 	github.com/opencoff/go-utils v0.3.0
 	github.com/opencoff/pflag v0.3.3
 	golang.org/x/crypto v0.0.0-20191002192127-34f69633bfdc
diff --git a/go.sum b/go.sum
index 4c67c65..e318adb 100644
--- a/go.sum
+++ b/go.sum
@@ -1,3 +1,7 @@
+github.com/gogo/protobuf v1.3.1 h1:DqDEcV5aeaTmdFBePNpYsp3FlcVH/2ISVVM9Qf8PSls=
+github.com/gogo/protobuf v1.3.1/go.mod h1:SlYgWuQ5SjCEi6WLHjHCa1yvBfUnHcTbrrZtXPKa29o=
+github.com/kisielk/errcheck v1.2.0/go.mod h1:/BMXB+zMLi60iA8Vv6Ksmxu/1UDYcXs4uQLJ+jE2L00=
+github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
 github.com/opencoff/go-utils v0.3.0 h1:/TQXjf50o3GSB9MItog5L8Gf4GWJ4B5+rmqjB4g2RZQ=
 github.com/opencoff/go-utils v0.3.0/go.mod h1:c+7QUAiCCHcNH6OGvsZ0fviG7cgse8Y3ucg+xy7sGXM=
 github.com/opencoff/pflag v0.3.3 h1:yohZkwYGPkB34WXvUQzU5GyLhImnjfePDARUaE8me3U=
@@ -11,6 +15,7 @@ golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5h
 golang.org/x/sys v0.0.0-20190412213103-97732733099d h1:+R4KGOnez64A81RvjARKc4UT5/tI9ujCIVX+P5KiHuI=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/tools v0.0.0-20181030221726-6c7e314b6563/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v2 v2.2.4 h1:/eiJrUcujPVeJ3xlSWaiNi3uSVmDGBK1pDHUHAnao1I=
 gopkg.in/yaml.v2 v2.2.4/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
diff --git a/sign/encrypt.go b/sign/encrypt.go
index db80852..a5877c6 100644
--- a/sign/encrypt.go
+++ b/sign/encrypt.go
@@ -17,98 +17,427 @@ import (
 	"crypto/aes"
 	"crypto/cipher"
 	"crypto/ed25519"
+	"crypto/sha256"
 	"crypto/sha512"
-	"encoding/hex"
+	"crypto/subtle"
 	"fmt"
 	"golang.org/x/crypto/curve25519"
 	"golang.org/x/crypto/hkdf"
 	"io"
 	"math/big"
-	"strings"
+	"bytes"
+	"encoding/binary"
 )
 
-// A File-encryption-key wrapped by the Ed25519 public key of the recipient
-type WrappedKey struct {
-	Key    []byte // KEK - wrapped with the Curve25519 PK of recipient
-	Pk     []byte // Curve25519 PK used to wrap
-	PkHash []byte // hash of the corresponding Ed25519 PK
+
+// Encryption chunk size = 4MB
+const chunkSize int = 4 * 1048576
+
+const _Magic = "SigTool"
+const _MagicLen = len(_Magic)
+const _AEADNonceLen = 32
+
+
+// Encryptor holds the encryption context
+type Encryptor struct {
+	Header
+	key [32]byte  // file encryption key
+
+	ae  cipher.AEAD
+	sender *PrivateKey
+	started bool
+
+	buf []byte
 }
 
-func hx(b []byte) string {
-	return hex.EncodeToString(b)
-}
+// Create a new Encryption context and use the optional private key 'sk' for 
+// signing any recipient keys. If 'sk' is nil, then ephmeral Curve25519 keys
+// are generated and used with recipient's public key.
+func NewEncryptor(sk *PrivateKey) (*Encryptor, error) {
 
-func unhx(s string) ([]byte, error) {
-	return hex.DecodeString(s)
-}
+	e := &Encryptor{
+		Header: Header{
+			ChunkSize: uint32(chunkSize),
+			Salt:	   make([]byte, _AEADNonceLen),
+		},
 
-func (w *WrappedKey) ToString() string {
-	return fmt.Sprintf("(ed25519 to=%x, pk=%x, kek=%x)",
-		hx(w.PkHash), hx(w.Pk), hx(w.Key))
-}
-
-func parseErr(s string, v ...interface{}) error {
-	return fmt.Errorf(s, v...)
-}
-
-// Given an marshalled stream of bytes, return the PubKey, encrypted key
-func ParseWrappedKey(s string) (*WrappedKey, error) {
-	s = strings.TrimSpace(s)
-	if s[0] != '(' {
-		return nil, parseErr("missing '(' in wrapped key")
+		sender: sk,
 	}
 
-	if s[len(s)-1] != ')' {
-		return nil, parseErr("missing ')' in wrapped key")
+	randread(e.key[:])
+	randread(e.Salt)
+
+	aes, err := aes.NewCipher(e.key[:])
+	if err != nil {
+		return nil, fmt.Errorf("encrypt: %s", err)
 	}
 
-	s = s[1 : len(s)-1]
-	v := strings.Fields(s)
-	if len(v) != 3 {
-		return nil, parseErr("Incorrect number of elements (exp 3, saw %d) in wrapped key", len(v))
+	e.ae, err = cipher.NewGCMWithNonceSize(aes, _AEADNonceLen)
+	if err != nil {
+		return nil, fmt.Errorf("encrypt: %s", err)
 	}
 
-	var w WrappedKey
+	e.buf = make([]byte, chunkSize + 4 + e.ae.Overhead())
+	return e, nil
+}
 
-	for _, z := range v {
-		kw := strings.Split(z, "=")
-		if len(kw) != 2 {
-			return nil, parseErr("malformed key=value pair (%s) in wrapped key", z)
-		}
 
-		var err error
-		switch strings.ToLower(kw[0]) {
-		case "to":
-			w.PkHash, err = unhx(kw[1])
+// Add a new recipient to this encryption context.
+func (e *Encryptor) AddRecipient(pk *PublicKey) error {
+	if e.started {
+		return fmt.Errorf("encrypt: can't add new recipient after encryption has started")
+	}
 
-		case "pk":
-			w.Pk, err = unhx(kw[1])
+	var w *WrappedKey
+	var err error
 
-		case "kek":
-			w.Key, err = unhx(kw[1])
+	if e.sender != nil {
+		w, err = e.sender.WrapKey(pk, e.key[:])
+	} else {
+		w, err = pk.WrapKeyEphemeral(e.key[:])
+	}
+	if err != nil {
+		return err
+	}
 
-		default:
-			return nil, parseErr("unknown keyword %s in wrapped key", kw[0])
-		}
+	e.Keys = append(e.Keys, w)
+	return nil
+}
 
+
+// Begin the encryption process by writing the header
+func (e *Encryptor) start(wr io.Writer) error {
+	msize := e.Size()
+
+	// marshal the header and recipients
+	hdrlen := _MagicLen + 1 + 4 + sha256.Size
+
+	buf := make([]byte, hdrlen + msize)
+	hdrbuf := buf[hdrlen:]
+
+	copy(buf[:], []byte(_Magic))
+
+	buf[_MagicLen] = 1  // file version#
+
+	// The fixed header is the magic _and _ the length of the variable segment.
+	// So, we capture the length of the variable portion first.
+	binary.BigEndian.PutUint32(buf[_MagicLen + 1:], uint32(sha256.Size + msize))
+
+	// Now marshal the variable portion
+	_, err := e.MarshalToSizedBuffer(hdrbuf)
+	if err != nil {
+		return fmt.Errorf("encrypt: can't marshal header: %s", err)
+	}
+
+	// and calculate the header checksum
+	cksum := buf[_MagicLen + 1 + 4:]
+	h := sha256.New()
+	h.Write(hdrbuf)
+	h.Sum(cksum[:0])
+
+	// Finally write it out
+	err = fullwrite(buf, wr)
+	if err != nil {
+		return fmt.Errorf("encrypt: %s", err)
+	}
+
+	e.started = true
+	return nil
+}
+
+// Write _all_ bytes of buffer 'buf'
+func fullwrite(buf []byte, wr io.Writer) error {
+	n := len(buf)
+
+	for n > 0 {
+		m, err := wr.Write(buf)
 		if err != nil {
-			return nil, parseErr("can't parse value for %s in wrapped key", kw[0])
+			return fmt.Errorf("I/O error: %s", err)
+		}
+
+		n -= m
+		buf = buf[m:]
+	}
+	return nil
+}
+
+
+// Encrypt the input stream 'rd' and write encrypted stream to 'wr'
+func (e *Encryptor) Encrypt(rd io.Reader, wr io.Writer) error {
+	if !e.started {
+		err := e.start(wr)
+		if err != nil {
+			return err
 		}
 	}
 
-	if len(w.PkHash) != 16 {
-		return nil, parseErr("invalid PkHash length (exp 16, saw %d) in wrapped key", len(w.PkHash))
+	buf := make([]byte, e.ChunkSize)
+	i := 0
+
+	for {
+		n, err := io.ReadAtLeast(rd, buf, int(e.ChunkSize))
+		if n == 0 {
+			return nil
+		}
+		if n > 0 {
+			err = e.encrypt(buf[:n], wr, i)
+			if err != nil {
+				return err
+			}
+
+			i++
+			continue
+		}
+
+		if err != nil && err != io.EOF {
+			return fmt.Errorf("encrypt: I/O read error: %s", err)
+		}
+	}
+}
+
+// encrypt exactly _one_ block of data
+// The nonce for the block is: sha256(salt || chunkLen || block#)
+// This protects the output stream from re-ordering attacks and length
+// modification attacks. The encoded length & block number is used as
+// additional data in the AEAD construction.
+func (e *Encryptor) encrypt(buf []byte, wr io.Writer, i int) error {
+	var b [8]byte
+	var noncebuf [32]byte
+
+	binary.BigEndian.PutUint32(b[:4], uint32(e.ae.Overhead() + len(buf)))
+	binary.BigEndian.PutUint32(b[4:], uint32(i))
+
+	h := sha256.New()
+	h.Write(e.Salt)
+	h.Write(b[:])
+	nonce := h.Sum(noncebuf[:0])
+
+	copy(e.buf[:4], b[:4])
+	cbuf := e.buf[4:]
+	c := e.ae.Seal(cbuf[:0], nonce, buf, b[:])
+
+	n := len(c) + 4
+
+	err := fullwrite(e.buf[:n], wr)
+	if err != nil {
+		return fmt.Errorf("encrypt: %s", err)
+	}
+	return nil
+}
+
+
+// Decryptor holds the decryption context
+type Decryptor struct {
+	Header
+
+	ae cipher.AEAD
+	rd io.Reader
+	buf []byte
+
+	// Decrypted key
+	key []byte
+}
+
+
+// Create a new decryption context and if 'pk' is given, check that it matches
+// the sender
+func NewDecryptor(rd io.Reader, pk *PublicKey) (*Decryptor, error) {
+	var  b [12]byte
+
+	_, err := io.ReadFull(rd,  b[:])
+	if err != nil {
+		return nil, err
 	}
 
-	if len(w.Pk) != 32 {
-		return nil, parseErr("invalid Public Key length (exp 32, saw %d) in wrapped key", len(w.Pk))
+	if bytes.Compare(b[:_MagicLen], []byte(_Magic)) != 0 {
+		return nil, fmt.Errorf("decrypt: Not a sigtool encrypted file?")
 	}
 
-	if len(w.Key) != 32 {
-		return nil, parseErr("invalid Key length (exp 32, saw %d) in wrapped key", len(w.Key))
+	if b[_MagicLen] != 1 {
+		return nil, fmt.Errorf("decrypt: Unsupported version %d", b[_MagicLen])
 	}
 
-	return &w, nil
+	hdrlen := binary.BigEndian.Uint32(b[_MagicLen+1:])
+	if hdrlen > 65536 {
+		return nil, fmt.Errorf("decrypt: header too large (max 65536)")
+	}
+	if hdrlen < 32 {
+		return nil, fmt.Errorf("decrypt: header too small (min 32)")
+	}
+
+	hdr := make([]byte, hdrlen)
+
+	_, err = io.ReadFull(rd, hdr)
+	if err != nil {
+		return nil, err
+	}
+
+	verify := hdr[:32]
+	hdr = hdr[32:]
+
+	cksum := sha256.Sum256(hdr)
+	if subtle.ConstantTimeCompare(verify, cksum[:]) == 0 {
+		return nil, fmt.Errorf("decrypt: header corrupted")
+	}
+
+	d := &Decryptor{
+		rd:  rd,
+	}
+
+	err = d.Header.Unmarshal(hdr)
+	if err != nil {
+		return nil, fmt.Errorf("decrypt: decode error: %s", err)
+	}
+
+	if d.ChunkSize == 0 || d.ChunkSize > (16 * 1048576) {
+		return nil, fmt.Errorf("decrypt: invalid chunkSize %d", d.ChunkSize)
+	}
+
+	if len(d.Salt) != 32 {
+		return nil, fmt.Errorf("decrypt: invalid nonce length %d", len(d.Salt))
+	}
+
+	if len(d.Keys) == 0 {
+		return nil, fmt.Errorf("decrypt: no wrapped keys")
+	}
+
+	// sanity check on the wrapped keys
+	for i, w := range d.Keys {
+		if len(w.PkHash) != PKHashLength {
+			return nil, fmt.Errorf("decrypt: wrapped key %d: invalid PkHash", i)
+		}
+
+		if len(w.Pk) != 32 {
+			return nil, fmt.Errorf("decrypt: wrapped key %d: invalid Curve25519 PK", i)
+		}
+
+		// XXX Default AES-256-GCM Nonce size is 12
+		if len(w.Nonce) != 12 {
+			return nil, fmt.Errorf("decrypt: wrapped key %d: invalid Nonce", i)
+		}
+
+		if len(w.Key) == 0 {
+			return nil, fmt.Errorf("decrypt: wrapped key %d: missing encrypted key", i)
+		}
+
+	}
+
+	d.buf = make([]byte, d.ChunkSize)
+	if pk != nil {
+		validSender := false
+		pkh := pk.Hash()
+		for _, w := range d.Keys {
+			if subtle.ConstantTimeCompare(pkh, w.PkHash) == 1 {
+				validSender = true
+			}
+		}
+
+		if !validSender {
+			return nil, fmt.Errorf("decrypt: Can't find sender's public key in the header")
+		}
+	}
+
+	return d, nil
+}
+
+// Use Private Key 'sk' to decrypt the encrypted keys in the header
+func (d *Decryptor) SetPrivateKey(sk *PrivateKey) error {
+	var err error
+
+	pkh := sk.PublicKey().Hash()
+	for i, w := range d.Keys {
+		if subtle.ConstantTimeCompare(pkh, w.PkHash) == 1 {
+			d.key, err = w.UnwrapKey(sk)
+			if err != nil {
+				return fmt.Errorf("decrypt: can't unwrap key %d: %s", i, err)
+			}
+			goto havekey
+		}
+	}
+
+	return fmt.Errorf("decrypt: Can't find any public key to match the given private key")
+
+
+havekey:
+	aes, err := aes.NewCipher(d.key)
+	if err != nil {
+		return fmt.Errorf("decrypt: %s", err)
+	}
+
+	d.ae, err = cipher.NewGCMWithNonceSize(aes, _AEADNonceLen)
+	if err != nil {
+		return fmt.Errorf("decrypt: %s", err)
+	}
+	return nil
+}
+
+// Return a list of Wrapped keys in the encrypted file header
+func (d *Decryptor) WrappedKeys() []*WrappedKey {
+	return d.Keys
+}
+
+
+// Decrypt the file and write to 'wr'
+func (d *Decryptor) Decrypt(wr io.Writer) error {
+	if d.key == nil {
+		return fmt.Errorf("decrypt: wrapped-key not decrypted (missing SetPrivateKey()?")
+	}
+
+	for i := 0; ; i++ {
+		c, err := d.decrypt(i)
+		if err != nil {
+			return err
+		}
+		if len(c) == 0 {
+			return nil
+		}
+		
+		if len(c) > 0 {
+			err = fullwrite(c, wr)
+			if err != nil {
+				return fmt.Errorf("decrypt: %s", err)
+			}
+		}
+	}
+	return nil
+}
+
+// Decrypt exactly one chunk of data
+func (d *Decryptor) decrypt(i int) ([]byte, error) {
+	var b [8]byte
+	var nonceb [32]byte
+
+	n, err := io.ReadFull(d.rd, b[:4])
+	if n == 0 || err == io.EOF {
+		return nil, nil
+	}
+
+	if err != nil {
+		return nil, fmt.Errorf("decrypt: can't read chunk %d length: %s", i, err)
+	}
+
+
+	chunklen := int(binary.BigEndian.Uint32(b[:4]))
+	binary.BigEndian.PutUint32(b[4:], uint32(i))
+	h := sha256.New()
+	h.Write(d.Salt)
+	h.Write(b[:])
+	nonce := h.Sum(nonceb[:0])
+
+	n, err = io.ReadFull(d.rd, d.buf[:chunklen])
+	if n == 0 || err == io.EOF {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, fmt.Errorf("decrypt: can't read chunk %d: %s", i, err)
+	}
+
+	p, err := d.ae.Open(d.buf[:0], nonce, d.buf[:chunklen], b[:])
+	if err != nil {
+		return nil, fmt.Errorf("decrypt: can't decrypt chunk %d: %s", i, err)
+	}
+
+	return p, nil
 }
 
 // given a file-encryption-key, wrap it in the identity of the recipient 'pk' using our
@@ -125,6 +454,23 @@ func (sk *PrivateKey) WrapKey(pk *PublicKey, key []byte) (*WrappedKey, error) {
 
 }
 
+// Unwrap a wrapped key using the private key 'sk'
+func (w *WrappedKey) UnwrapKey(sk *PrivateKey) ([]byte, error) {
+	var shared, theirPK, ourSK [32]byte
+
+	pk := sk.PublicKey()
+	copy(ourSK[:], sk.toCurve25519SK())
+	copy(theirPK[:], w.Pk)
+	curve25519.ScalarMult(&shared, &ourSK, &theirPK)
+
+	key, err := aeadOpen(w.Key, w.Nonce, shared[:], pk.Pk)
+	if err != nil {
+		return nil, err
+	}
+	return key, nil
+}
+
+
 // Wrap a shared key with the recipient's public key 'pk' by generating an ephemeral
 // Curve25519 keypair. This function does not identify the sender (non-repudiation).
 func (pk *PublicKey) WrapKeyEphemeral(key []byte) (*WrappedKey, error) {
@@ -144,22 +490,16 @@ func (pk *PublicKey) WrapKeyEphemeral(key []byte) (*WrappedKey, error) {
 }
 
 func wrapKey(pk *PublicKey, k, theirPK, shared []byte) (*WrappedKey, error) {
-
-	// hkdf or HMAC-sha-256
-	kek, err := expand(shared[:], pk.Pk)
-	if err != nil {
-		return nil, fmt.Errorf("wrap: %s", err)
-	}
-
-	ek, err := aeadSeal(k, kek)
+	ek, nonce, err := aeadSeal(k, shared[:], pk.Pk)
 	if err != nil {
 		return nil, fmt.Errorf("wrap: %s", err)
 	}
 
 	return &WrappedKey{
-		Key:    ek,
-		Pk:     theirPK,
 		PkHash: pk.hash,
+		Pk:     theirPK,
+		Nonce:  nonce,
+		Key:    ek,
 	}, nil
 }
 
@@ -226,67 +566,65 @@ func expand(shared, pk []byte) ([]byte, error) {
 	return kek, err
 }
 
-func aeadSeal(data, key []byte) ([]byte, error) {
-	var salt [32]byte
-	var nonceb [64]byte
 
-	randread(salt[:])
-
-	h := sha512.New()
-	h.Write(salt[:])
-	h.Write(key)
-	nonce := h.Sum(nonceb[:0])[:32]
-
-	aes, err := aes.NewCipher(key)
+// seal the data via AEAD after suitably expanding 'shared' 
+func aeadSeal(data, shared, pk []byte) ([]byte, []byte, error) {
+	kek, err := expand(shared[:], pk)
 	if err != nil {
-		return nil, err
+		return nil, nil, fmt.Errorf("wrap: %s", err)
 	}
 
-	ae, err := cipher.NewGCMWithNonceSize(aes, len(nonce))
+	aes, err := aes.NewCipher(kek)
 	if err != nil {
-		return nil, err
+		return nil, nil, fmt.Errorf("wrap: %s", err)
+	}
+
+	ae, err := cipher.NewGCM(aes)
+	if err != nil {
+		return nil, nil, fmt.Errorf("wrap: %s", err)
+	}
+
+	noncesize := ae.NonceSize()
+	tagsize := ae.Overhead()
+
+	buf := make([]byte, tagsize + len(kek))
+	nonce := make([]byte, noncesize)
+
+	randread(nonce)
+
+	out := ae.Seal(buf[:0], nonce, data, nil)
+	return out, nonce, nil
+}
+
+func aeadOpen(data, nonce, shared, pk []byte) ([]byte, error) {
+	// hkdf or HMAC-sha-256
+	kek, err := expand(shared, pk)
+	if err != nil {
+		return nil, fmt.Errorf("unwrap: %s", err)
+	}
+	aes, err := aes.NewCipher(kek)
+	if err != nil {
+		return nil, fmt.Errorf("unwrap: %s", err)
+	}
+
+	ae, err := cipher.NewGCM(aes)
+	if err != nil {
+		return nil, fmt.Errorf("unwrap: %s", err)
+	}
+
+	want := 32 + ae.Overhead()
+	if len(data) != want {
+		return nil, fmt.Errorf("unwrap: incorrect decrypt bytes (need %d, saw %d)", want, len(data))
+	}
+
+	c, err := ae.Open(data[:0], nonce, data, nil)
+	if err != nil {
+		return nil, fmt.Errorf("unwrap: %s", err)
 	}
 
-	c := ae.Seal(nil, nonce, data, nil)
-	c = append(c, salt[:]...)
 	return c, nil
 }
 
-func aeadOpen(data, key []byte) ([]byte, error) {
-	var nonceb [64]byte
-	// GCM tag: 16 bytes
-	// salt: 32 bytes
-	// last 32 bytes: salt
-
-	n := len(data)
-	if n < (32 + 16) {
-		return nil, fmt.Errorf("aead: too few decrypt bytes (min 48, saw %d)", n)
-	}
-
-	salt := data[n-32:]
-	data = data[:n-32]
-
-	h := sha512.New()
-	h.Write(salt)
-	h.Write(key)
-	nonce := h.Sum(nonceb[:0])[:32]
-
-	aes, err := aes.NewCipher(key)
-	if err != nil {
-		return nil, err
-	}
-
-	ae, err := cipher.NewGCMWithNonceSize(aes, len(nonce))
-	if err != nil {
-		return nil, err
-	}
-
-	c, err := ae.Open(nil, nonce, data, nil)
-	if err != nil {
-		return nil, err
-	}
-	return c, nil
-}
 
 func clamp(k []byte) []byte {
 	k[0] &= 248
diff --git a/sign/hdr.pb.go b/sign/hdr.pb.go
new file mode 100644
index 0000000..eb45149
--- /dev/null
+++ b/sign/hdr.pb.go
@@ -0,0 +1,899 @@
+// Code generated by protoc-gen-gogo. DO NOT EDIT.
+// source: sign/hdr.proto
+
+package sign
+
+import (
+	bytes "bytes"
+	fmt "fmt"
+	proto "github.com/gogo/protobuf/proto"
+	io "io"
+	math "math"
+	math_bits "math/bits"
+	reflect "reflect"
+	strings "strings"
+)
+
+// Reference imports to suppress errors if they are not otherwise used.
+var _ = proto.Marshal
+var _ = fmt.Errorf
+var _ = math.Inf
+
+// This is a compile-time assertion to ensure that this generated file
+// is compatible with the proto package it is being compiled against.
+// A compilation error at this line likely means your copy of the
+// proto package needs to be updated.
+const _ = proto.GoGoProtoPackageIsVersion3 // please upgrade the proto package
+
+type Header struct {
+	ChunkSize uint32        `protobuf:"varint,1,opt,name=chunk_size,json=chunkSize,proto3" json:"chunk_size,omitempty"`
+	Salt      []byte        `protobuf:"bytes,2,opt,name=salt,proto3" json:"salt,omitempty"`
+	Keys      []*WrappedKey `protobuf:"bytes,3,rep,name=keys,proto3" json:"keys,omitempty"`
+}
+
+func (m *Header) Reset()      { *m = Header{} }
+func (*Header) ProtoMessage() {}
+func (*Header) Descriptor() ([]byte, []int) {
+	return fileDescriptor_85aff542c746609f, []int{0}
+}
+func (m *Header) XXX_Unmarshal(b []byte) error {
+	return m.Unmarshal(b)
+}
+func (m *Header) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	if deterministic {
+		return xxx_messageInfo_Header.Marshal(b, m, deterministic)
+	} else {
+		b = b[:cap(b)]
+		n, err := m.MarshalToSizedBuffer(b)
+		if err != nil {
+			return nil, err
+		}
+		return b[:n], nil
+	}
+}
+func (m *Header) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_Header.Merge(m, src)
+}
+func (m *Header) XXX_Size() int {
+	return m.Size()
+}
+func (m *Header) XXX_DiscardUnknown() {
+	xxx_messageInfo_Header.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_Header proto.InternalMessageInfo
+
+func (m *Header) GetChunkSize() uint32 {
+	if m != nil {
+		return m.ChunkSize
+	}
+	return 0
+}
+
+func (m *Header) GetSalt() []byte {
+	if m != nil {
+		return m.Salt
+	}
+	return nil
+}
+
+func (m *Header) GetKeys() []*WrappedKey {
+	if m != nil {
+		return m.Keys
+	}
+	return nil
+}
+
+type WrappedKey struct {
+	PkHash []byte `protobuf:"bytes,1,opt,name=pk_hash,json=pkHash,proto3" json:"pk_hash,omitempty"`
+	Pk     []byte `protobuf:"bytes,2,opt,name=pk,proto3" json:"pk,omitempty"`
+	Nonce  []byte `protobuf:"bytes,3,opt,name=nonce,proto3" json:"nonce,omitempty"`
+	Key    []byte `protobuf:"bytes,4,opt,name=key,proto3" json:"key,omitempty"`
+}
+
+func (m *WrappedKey) Reset()      { *m = WrappedKey{} }
+func (*WrappedKey) ProtoMessage() {}
+func (*WrappedKey) Descriptor() ([]byte, []int) {
+	return fileDescriptor_85aff542c746609f, []int{1}
+}
+func (m *WrappedKey) XXX_Unmarshal(b []byte) error {
+	return m.Unmarshal(b)
+}
+func (m *WrappedKey) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	if deterministic {
+		return xxx_messageInfo_WrappedKey.Marshal(b, m, deterministic)
+	} else {
+		b = b[:cap(b)]
+		n, err := m.MarshalToSizedBuffer(b)
+		if err != nil {
+			return nil, err
+		}
+		return b[:n], nil
+	}
+}
+func (m *WrappedKey) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_WrappedKey.Merge(m, src)
+}
+func (m *WrappedKey) XXX_Size() int {
+	return m.Size()
+}
+func (m *WrappedKey) XXX_DiscardUnknown() {
+	xxx_messageInfo_WrappedKey.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_WrappedKey proto.InternalMessageInfo
+
+func (m *WrappedKey) GetPkHash() []byte {
+	if m != nil {
+		return m.PkHash
+	}
+	return nil
+}
+
+func (m *WrappedKey) GetPk() []byte {
+	if m != nil {
+		return m.Pk
+	}
+	return nil
+}
+
+func (m *WrappedKey) GetNonce() []byte {
+	if m != nil {
+		return m.Nonce
+	}
+	return nil
+}
+
+func (m *WrappedKey) GetKey() []byte {
+	if m != nil {
+		return m.Key
+	}
+	return nil
+}
+
+func init() {
+	proto.RegisterType((*Header)(nil), "sign.header")
+	proto.RegisterType((*WrappedKey)(nil), "sign.wrapped_key")
+}
+
+func init() { proto.RegisterFile("sign/hdr.proto", fileDescriptor_85aff542c746609f) }
+
+var fileDescriptor_85aff542c746609f = []byte{
+	// 257 bytes of a gzipped FileDescriptorProto
+	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0x4c, 0x90, 0x31, 0x4a, 0xc4, 0x40,
+	0x14, 0x86, 0xe7, 0x25, 0x31, 0xe2, 0xdb, 0x75, 0xd1, 0x41, 0x30, 0x8d, 0x8f, 0xb0, 0x20, 0xa4,
+	0x8a, 0xa0, 0x9e, 0xc0, 0xca, 0x3a, 0xf6, 0x86, 0xec, 0x66, 0x70, 0xc2, 0x48, 0x32, 0x64, 0x56,
+	0x24, 0x5b, 0x79, 0x04, 0x8f, 0xe1, 0x51, 0x2c, 0x53, 0x6e, 0x69, 0x26, 0x8d, 0xe5, 0x1e, 0x41,
+	0x32, 0x5a, 0xd8, 0xfd, 0xff, 0xf7, 0xe0, 0x7d, 0xf0, 0xe3, 0xc2, 0x54, 0x4f, 0xf5, 0x95, 0x2c,
+	0xdb, 0x54, 0xb7, 0xcd, 0xa6, 0xe1, 0xc1, 0xd4, 0x97, 0x2b, 0x0c, 0xa5, 0x28, 0x4a, 0xd1, 0xf2,
+	0x0b, 0xc4, 0xb5, 0x7c, 0xa9, 0x55, 0x6e, 0xaa, 0xad, 0x88, 0x20, 0x86, 0xe4, 0x38, 0x3b, 0x72,
+	0xe4, 0xa1, 0xda, 0x0a, 0xce, 0x31, 0x30, 0xc5, 0xf3, 0x26, 0xf2, 0x62, 0x48, 0xe6, 0x99, 0xcb,
+	0xfc, 0x12, 0x03, 0x25, 0x3a, 0x13, 0xf9, 0xb1, 0x9f, 0xcc, 0xae, 0x4f, 0xd3, 0xe9, 0x63, 0xfa,
+	0xda, 0x16, 0x5a, 0x8b, 0x32, 0x57, 0xa2, 0xcb, 0xdc, 0x79, 0xf9, 0x88, 0xb3, 0x7f, 0x90, 0x9f,
+	0xe3, 0xa1, 0x56, 0xb9, 0x2c, 0x8c, 0x74, 0x96, 0x79, 0x16, 0x6a, 0x75, 0x5f, 0x18, 0xc9, 0x17,
+	0xe8, 0x69, 0xf5, 0x27, 0xf0, 0xb4, 0xe2, 0x67, 0x78, 0x50, 0x37, 0xf5, 0x5a, 0x44, 0xbe, 0x43,
+	0xbf, 0x85, 0x9f, 0xa0, 0xaf, 0x44, 0x17, 0x05, 0x8e, 0x4d, 0xf1, 0xee, 0xb6, 0x1f, 0x88, 0xed,
+	0x06, 0x62, 0xfb, 0x81, 0xe0, 0xcd, 0x12, 0x7c, 0x58, 0x82, 0x4f, 0x4b, 0xd0, 0x5b, 0x82, 0x2f,
+	0x4b, 0xf0, 0x6d, 0x89, 0xed, 0x2d, 0xc1, 0xfb, 0x48, 0xac, 0x1f, 0x89, 0xed, 0x46, 0x62, 0xab,
+	0xd0, 0xcd, 0x70, 0xf3, 0x13, 0x00, 0x00, 0xff, 0xff, 0xde, 0xf2, 0x28, 0xc0, 0x18, 0x01, 0x00,
+	0x00,
+}
+
+func (this *Header) Equal(that interface{}) bool {
+	if that == nil {
+		return this == nil
+	}
+
+	that1, ok := that.(*Header)
+	if !ok {
+		that2, ok := that.(Header)
+		if ok {
+			that1 = &that2
+		} else {
+			return false
+		}
+	}
+	if that1 == nil {
+		return this == nil
+	} else if this == nil {
+		return false
+	}
+	if this.ChunkSize != that1.ChunkSize {
+		return false
+	}
+	if !bytes.Equal(this.Salt, that1.Salt) {
+		return false
+	}
+	if len(this.Keys) != len(that1.Keys) {
+		return false
+	}
+	for i := range this.Keys {
+		if !this.Keys[i].Equal(that1.Keys[i]) {
+			return false
+		}
+	}
+	return true
+}
+func (this *WrappedKey) Equal(that interface{}) bool {
+	if that == nil {
+		return this == nil
+	}
+
+	that1, ok := that.(*WrappedKey)
+	if !ok {
+		that2, ok := that.(WrappedKey)
+		if ok {
+			that1 = &that2
+		} else {
+			return false
+		}
+	}
+	if that1 == nil {
+		return this == nil
+	} else if this == nil {
+		return false
+	}
+	if !bytes.Equal(this.PkHash, that1.PkHash) {
+		return false
+	}
+	if !bytes.Equal(this.Pk, that1.Pk) {
+		return false
+	}
+	if !bytes.Equal(this.Nonce, that1.Nonce) {
+		return false
+	}
+	if !bytes.Equal(this.Key, that1.Key) {
+		return false
+	}
+	return true
+}
+func (this *Header) GoString() string {
+	if this == nil {
+		return "nil"
+	}
+	s := make([]string, 0, 7)
+	s = append(s, "&sign.Header{")
+	s = append(s, "ChunkSize: "+fmt.Sprintf("%#v", this.ChunkSize)+",\n")
+	s = append(s, "Salt: "+fmt.Sprintf("%#v", this.Salt)+",\n")
+	if this.Keys != nil {
+		s = append(s, "Keys: "+fmt.Sprintf("%#v", this.Keys)+",\n")
+	}
+	s = append(s, "}")
+	return strings.Join(s, "")
+}
+func (this *WrappedKey) GoString() string {
+	if this == nil {
+		return "nil"
+	}
+	s := make([]string, 0, 8)
+	s = append(s, "&sign.WrappedKey{")
+	s = append(s, "PkHash: "+fmt.Sprintf("%#v", this.PkHash)+",\n")
+	s = append(s, "Pk: "+fmt.Sprintf("%#v", this.Pk)+",\n")
+	s = append(s, "Nonce: "+fmt.Sprintf("%#v", this.Nonce)+",\n")
+	s = append(s, "Key: "+fmt.Sprintf("%#v", this.Key)+",\n")
+	s = append(s, "}")
+	return strings.Join(s, "")
+}
+func valueToGoStringHdr(v interface{}, typ string) string {
+	rv := reflect.ValueOf(v)
+	if rv.IsNil() {
+		return "nil"
+	}
+	pv := reflect.Indirect(rv).Interface()
+	return fmt.Sprintf("func(v %v) *%v { return &v } ( %#v )", typ, typ, pv)
+}
+func (m *Header) Marshal() (dAtA []byte, err error) {
+	size := m.Size()
+	dAtA = make([]byte, size)
+	n, err := m.MarshalToSizedBuffer(dAtA[:size])
+	if err != nil {
+		return nil, err
+	}
+	return dAtA[:n], nil
+}
+
+func (m *Header) MarshalTo(dAtA []byte) (int, error) {
+	size := m.Size()
+	return m.MarshalToSizedBuffer(dAtA[:size])
+}
+
+func (m *Header) MarshalToSizedBuffer(dAtA []byte) (int, error) {
+	i := len(dAtA)
+	_ = i
+	var l int
+	_ = l
+	if len(m.Keys) > 0 {
+		for iNdEx := len(m.Keys) - 1; iNdEx >= 0; iNdEx-- {
+			{
+				size, err := m.Keys[iNdEx].MarshalToSizedBuffer(dAtA[:i])
+				if err != nil {
+					return 0, err
+				}
+				i -= size
+				i = encodeVarintHdr(dAtA, i, uint64(size))
+			}
+			i--
+			dAtA[i] = 0x1a
+		}
+	}
+	if len(m.Salt) > 0 {
+		i -= len(m.Salt)
+		copy(dAtA[i:], m.Salt)
+		i = encodeVarintHdr(dAtA, i, uint64(len(m.Salt)))
+		i--
+		dAtA[i] = 0x12
+	}
+	if m.ChunkSize != 0 {
+		i = encodeVarintHdr(dAtA, i, uint64(m.ChunkSize))
+		i--
+		dAtA[i] = 0x8
+	}
+	return len(dAtA) - i, nil
+}
+
+func (m *WrappedKey) Marshal() (dAtA []byte, err error) {
+	size := m.Size()
+	dAtA = make([]byte, size)
+	n, err := m.MarshalToSizedBuffer(dAtA[:size])
+	if err != nil {
+		return nil, err
+	}
+	return dAtA[:n], nil
+}
+
+func (m *WrappedKey) MarshalTo(dAtA []byte) (int, error) {
+	size := m.Size()
+	return m.MarshalToSizedBuffer(dAtA[:size])
+}
+
+func (m *WrappedKey) MarshalToSizedBuffer(dAtA []byte) (int, error) {
+	i := len(dAtA)
+	_ = i
+	var l int
+	_ = l
+	if len(m.Key) > 0 {
+		i -= len(m.Key)
+		copy(dAtA[i:], m.Key)
+		i = encodeVarintHdr(dAtA, i, uint64(len(m.Key)))
+		i--
+		dAtA[i] = 0x22
+	}
+	if len(m.Nonce) > 0 {
+		i -= len(m.Nonce)
+		copy(dAtA[i:], m.Nonce)
+		i = encodeVarintHdr(dAtA, i, uint64(len(m.Nonce)))
+		i--
+		dAtA[i] = 0x1a
+	}
+	if len(m.Pk) > 0 {
+		i -= len(m.Pk)
+		copy(dAtA[i:], m.Pk)
+		i = encodeVarintHdr(dAtA, i, uint64(len(m.Pk)))
+		i--
+		dAtA[i] = 0x12
+	}
+	if len(m.PkHash) > 0 {
+		i -= len(m.PkHash)
+		copy(dAtA[i:], m.PkHash)
+		i = encodeVarintHdr(dAtA, i, uint64(len(m.PkHash)))
+		i--
+		dAtA[i] = 0xa
+	}
+	return len(dAtA) - i, nil
+}
+
+func encodeVarintHdr(dAtA []byte, offset int, v uint64) int {
+	offset -= sovHdr(v)
+	base := offset
+	for v >= 1<<7 {
+		dAtA[offset] = uint8(v&0x7f | 0x80)
+		v >>= 7
+		offset++
+	}
+	dAtA[offset] = uint8(v)
+	return base
+}
+func (m *Header) Size() (n int) {
+	if m == nil {
+		return 0
+	}
+	var l int
+	_ = l
+	if m.ChunkSize != 0 {
+		n += 1 + sovHdr(uint64(m.ChunkSize))
+	}
+	l = len(m.Salt)
+	if l > 0 {
+		n += 1 + l + sovHdr(uint64(l))
+	}
+	if len(m.Keys) > 0 {
+		for _, e := range m.Keys {
+			l = e.Size()
+			n += 1 + l + sovHdr(uint64(l))
+		}
+	}
+	return n
+}
+
+func (m *WrappedKey) Size() (n int) {
+	if m == nil {
+		return 0
+	}
+	var l int
+	_ = l
+	l = len(m.PkHash)
+	if l > 0 {
+		n += 1 + l + sovHdr(uint64(l))
+	}
+	l = len(m.Pk)
+	if l > 0 {
+		n += 1 + l + sovHdr(uint64(l))
+	}
+	l = len(m.Nonce)
+	if l > 0 {
+		n += 1 + l + sovHdr(uint64(l))
+	}
+	l = len(m.Key)
+	if l > 0 {
+		n += 1 + l + sovHdr(uint64(l))
+	}
+	return n
+}
+
+func sovHdr(x uint64) (n int) {
+	return (math_bits.Len64(x|1) + 6) / 7
+}
+func sozHdr(x uint64) (n int) {
+	return sovHdr(uint64((x << 1) ^ uint64((int64(x) >> 63))))
+}
+func (this *Header) String() string {
+	if this == nil {
+		return "nil"
+	}
+	repeatedStringForKeys := "[]*WrappedKey{"
+	for _, f := range this.Keys {
+		repeatedStringForKeys += strings.Replace(fmt.Sprintf("%v", f), "WrappedKey", "WrappedKey", 1) + ","
+	}
+	repeatedStringForKeys += "}"
+	s := strings.Join([]string{`&Header{`,
+		`ChunkSize:` + fmt.Sprintf("%v", this.ChunkSize) + `,`,
+		`Salt:` + fmt.Sprintf("%v", this.Salt) + `,`,
+		`Keys:` + repeatedStringForKeys + `,`,
+		`}`,
+	}, "")
+	return s
+}
+func (this *WrappedKey) String() string {
+	if this == nil {
+		return "nil"
+	}
+	s := strings.Join([]string{`&WrappedKey{`,
+		`PkHash:` + fmt.Sprintf("%v", this.PkHash) + `,`,
+		`Pk:` + fmt.Sprintf("%v", this.Pk) + `,`,
+		`Nonce:` + fmt.Sprintf("%v", this.Nonce) + `,`,
+		`Key:` + fmt.Sprintf("%v", this.Key) + `,`,
+		`}`,
+	}, "")
+	return s
+}
+func valueToStringHdr(v interface{}) string {
+	rv := reflect.ValueOf(v)
+	if rv.IsNil() {
+		return "nil"
+	}
+	pv := reflect.Indirect(rv).Interface()
+	return fmt.Sprintf("*%v", pv)
+}
+func (m *Header) Unmarshal(dAtA []byte) error {
+	l := len(dAtA)
+	iNdEx := 0
+	for iNdEx < l {
+		preIndex := iNdEx
+		var wire uint64
+		for shift := uint(0); ; shift += 7 {
+			if shift >= 64 {
+				return ErrIntOverflowHdr
+			}
+			if iNdEx >= l {
+				return io.ErrUnexpectedEOF
+			}
+			b := dAtA[iNdEx]
+			iNdEx++
+			wire |= uint64(b&0x7F) << shift
+			if b < 0x80 {
+				break
+			}
+		}
+		fieldNum := int32(wire >> 3)
+		wireType := int(wire & 0x7)
+		if wireType == 4 {
+			return fmt.Errorf("proto: header: wiretype end group for non-group")
+		}
+		if fieldNum <= 0 {
+			return fmt.Errorf("proto: header: illegal tag %d (wire type %d)", fieldNum, wire)
+		}
+		switch fieldNum {
+		case 1:
+			if wireType != 0 {
+				return fmt.Errorf("proto: wrong wireType = %d for field ChunkSize", wireType)
+			}
+			m.ChunkSize = 0
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowHdr
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				m.ChunkSize |= uint32(b&0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+		case 2:
+			if wireType != 2 {
+				return fmt.Errorf("proto: wrong wireType = %d for field Salt", wireType)
+			}
+			var byteLen int
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowHdr
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				byteLen |= int(b&0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			if byteLen < 0 {
+				return ErrInvalidLengthHdr
+			}
+			postIndex := iNdEx + byteLen
+			if postIndex < 0 {
+				return ErrInvalidLengthHdr
+			}
+			if postIndex > l {
+				return io.ErrUnexpectedEOF
+			}
+			m.Salt = append(m.Salt[:0], dAtA[iNdEx:postIndex]...)
+			if m.Salt == nil {
+				m.Salt = []byte{}
+			}
+			iNdEx = postIndex
+		case 3:
+			if wireType != 2 {
+				return fmt.Errorf("proto: wrong wireType = %d for field Keys", wireType)
+			}
+			var msglen int
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowHdr
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				msglen |= int(b&0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			if msglen < 0 {
+				return ErrInvalidLengthHdr
+			}
+			postIndex := iNdEx + msglen
+			if postIndex < 0 {
+				return ErrInvalidLengthHdr
+			}
+			if postIndex > l {
+				return io.ErrUnexpectedEOF
+			}
+			m.Keys = append(m.Keys, &WrappedKey{})
+			if err := m.Keys[len(m.Keys)-1].Unmarshal(dAtA[iNdEx:postIndex]); err != nil {
+				return err
+			}
+			iNdEx = postIndex
+		default:
+			iNdEx = preIndex
+			skippy, err := skipHdr(dAtA[iNdEx:])
+			if err != nil {
+				return err
+			}
+			if skippy < 0 {
+				return ErrInvalidLengthHdr
+			}
+			if (iNdEx + skippy) < 0 {
+				return ErrInvalidLengthHdr
+			}
+			if (iNdEx + skippy) > l {
+				return io.ErrUnexpectedEOF
+			}
+			iNdEx += skippy
+		}
+	}
+
+	if iNdEx > l {
+		return io.ErrUnexpectedEOF
+	}
+	return nil
+}
+func (m *WrappedKey) Unmarshal(dAtA []byte) error {
+	l := len(dAtA)
+	iNdEx := 0
+	for iNdEx < l {
+		preIndex := iNdEx
+		var wire uint64
+		for shift := uint(0); ; shift += 7 {
+			if shift >= 64 {
+				return ErrIntOverflowHdr
+			}
+			if iNdEx >= l {
+				return io.ErrUnexpectedEOF
+			}
+			b := dAtA[iNdEx]
+			iNdEx++
+			wire |= uint64(b&0x7F) << shift
+			if b < 0x80 {
+				break
+			}
+		}
+		fieldNum := int32(wire >> 3)
+		wireType := int(wire & 0x7)
+		if wireType == 4 {
+			return fmt.Errorf("proto: wrapped_key: wiretype end group for non-group")
+		}
+		if fieldNum <= 0 {
+			return fmt.Errorf("proto: wrapped_key: illegal tag %d (wire type %d)", fieldNum, wire)
+		}
+		switch fieldNum {
+		case 1:
+			if wireType != 2 {
+				return fmt.Errorf("proto: wrong wireType = %d for field PkHash", wireType)
+			}
+			var byteLen int
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowHdr
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				byteLen |= int(b&0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			if byteLen < 0 {
+				return ErrInvalidLengthHdr
+			}
+			postIndex := iNdEx + byteLen
+			if postIndex < 0 {
+				return ErrInvalidLengthHdr
+			}
+			if postIndex > l {
+				return io.ErrUnexpectedEOF
+			}
+			m.PkHash = append(m.PkHash[:0], dAtA[iNdEx:postIndex]...)
+			if m.PkHash == nil {
+				m.PkHash = []byte{}
+			}
+			iNdEx = postIndex
+		case 2:
+			if wireType != 2 {
+				return fmt.Errorf("proto: wrong wireType = %d for field Pk", wireType)
+			}
+			var byteLen int
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowHdr
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				byteLen |= int(b&0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			if byteLen < 0 {
+				return ErrInvalidLengthHdr
+			}
+			postIndex := iNdEx + byteLen
+			if postIndex < 0 {
+				return ErrInvalidLengthHdr
+			}
+			if postIndex > l {
+				return io.ErrUnexpectedEOF
+			}
+			m.Pk = append(m.Pk[:0], dAtA[iNdEx:postIndex]...)
+			if m.Pk == nil {
+				m.Pk = []byte{}
+			}
+			iNdEx = postIndex
+		case 3:
+			if wireType != 2 {
+				return fmt.Errorf("proto: wrong wireType = %d for field Nonce", wireType)
+			}
+			var byteLen int
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowHdr
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				byteLen |= int(b&0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			if byteLen < 0 {
+				return ErrInvalidLengthHdr
+			}
+			postIndex := iNdEx + byteLen
+			if postIndex < 0 {
+				return ErrInvalidLengthHdr
+			}
+			if postIndex > l {
+				return io.ErrUnexpectedEOF
+			}
+			m.Nonce = append(m.Nonce[:0], dAtA[iNdEx:postIndex]...)
+			if m.Nonce == nil {
+				m.Nonce = []byte{}
+			}
+			iNdEx = postIndex
+		case 4:
+			if wireType != 2 {
+				return fmt.Errorf("proto: wrong wireType = %d for field Key", wireType)
+			}
+			var byteLen int
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return ErrIntOverflowHdr
+				}
+				if iNdEx >= l {
+					return io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				byteLen |= int(b&0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			if byteLen < 0 {
+				return ErrInvalidLengthHdr
+			}
+			postIndex := iNdEx + byteLen
+			if postIndex < 0 {
+				return ErrInvalidLengthHdr
+			}
+			if postIndex > l {
+				return io.ErrUnexpectedEOF
+			}
+			m.Key = append(m.Key[:0], dAtA[iNdEx:postIndex]...)
+			if m.Key == nil {
+				m.Key = []byte{}
+			}
+			iNdEx = postIndex
+		default:
+			iNdEx = preIndex
+			skippy, err := skipHdr(dAtA[iNdEx:])
+			if err != nil {
+				return err
+			}
+			if skippy < 0 {
+				return ErrInvalidLengthHdr
+			}
+			if (iNdEx + skippy) < 0 {
+				return ErrInvalidLengthHdr
+			}
+			if (iNdEx + skippy) > l {
+				return io.ErrUnexpectedEOF
+			}
+			iNdEx += skippy
+		}
+	}
+
+	if iNdEx > l {
+		return io.ErrUnexpectedEOF
+	}
+	return nil
+}
+func skipHdr(dAtA []byte) (n int, err error) {
+	l := len(dAtA)
+	iNdEx := 0
+	depth := 0
+	for iNdEx < l {
+		var wire uint64
+		for shift := uint(0); ; shift += 7 {
+			if shift >= 64 {
+				return 0, ErrIntOverflowHdr
+			}
+			if iNdEx >= l {
+				return 0, io.ErrUnexpectedEOF
+			}
+			b := dAtA[iNdEx]
+			iNdEx++
+			wire |= (uint64(b) & 0x7F) << shift
+			if b < 0x80 {
+				break
+			}
+		}
+		wireType := int(wire & 0x7)
+		switch wireType {
+		case 0:
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return 0, ErrIntOverflowHdr
+				}
+				if iNdEx >= l {
+					return 0, io.ErrUnexpectedEOF
+				}
+				iNdEx++
+				if dAtA[iNdEx-1] < 0x80 {
+					break
+				}
+			}
+		case 1:
+			iNdEx += 8
+		case 2:
+			var length int
+			for shift := uint(0); ; shift += 7 {
+				if shift >= 64 {
+					return 0, ErrIntOverflowHdr
+				}
+				if iNdEx >= l {
+					return 0, io.ErrUnexpectedEOF
+				}
+				b := dAtA[iNdEx]
+				iNdEx++
+				length |= (int(b) & 0x7F) << shift
+				if b < 0x80 {
+					break
+				}
+			}
+			if length < 0 {
+				return 0, ErrInvalidLengthHdr
+			}
+			iNdEx += length
+		case 3:
+			depth++
+		case 4:
+			if depth == 0 {
+				return 0, ErrUnexpectedEndOfGroupHdr
+			}
+			depth--
+		case 5:
+			iNdEx += 4
+		default:
+			return 0, fmt.Errorf("proto: illegal wireType %d", wireType)
+		}
+		if iNdEx < 0 {
+			return 0, ErrInvalidLengthHdr
+		}
+		if depth == 0 {
+			return iNdEx, nil
+		}
+	}
+	return 0, io.ErrUnexpectedEOF
+}
+
+var (
+	ErrInvalidLengthHdr        = fmt.Errorf("proto: negative length found during unmarshaling")
+	ErrIntOverflowHdr          = fmt.Errorf("proto: integer overflow")
+	ErrUnexpectedEndOfGroupHdr = fmt.Errorf("proto: unexpected end of group")
+)
diff --git a/sign/hdr.proto b/sign/hdr.proto
new file mode 100644
index 0000000..509312a
--- /dev/null
+++ b/sign/hdr.proto
@@ -0,0 +1,23 @@
+syntax="proto3";
+
+//import "gogoproto/gogo.proto"
+
+package sign;
+
+//option (gogoproto.marshaler_all) = true;
+//option (gogoproto.sizer_all) = true;
+//option (gogoproto.unmarshaler_all) = true;
+//option (gogoproto.goproto_getters_all) = false;
+
+message header {
+	uint32 chunk_size = 1;
+	bytes  salt = 2;
+	repeated wrapped_key keys = 3;
+}
+
+message wrapped_key {
+	bytes pk_hash = 1; // hash of Ed25519 PK
+	bytes pk = 2;	    // curve25519 PK
+	bytes nonce = 3;    // AEAD nonce
+	bytes key = 4;	    // AEAD encrypted key
+}
diff --git a/sign/sign.go b/sign/sign.go
index 0e8fab3..87d08ef 100644
--- a/sign/sign.go
+++ b/sign/sign.go
@@ -77,6 +77,9 @@ type Signature struct {
 const sk_algo = "scrypt-sha256"
 const sig_algo = "sha512-ed25519"
 
+// Length of Ed25519 Public Key Hash
+const PKHashLength = 16
+
 // Scrypt parameters
 const _N = 1 << 17
 const _r = 16
@@ -132,7 +135,7 @@ type signature struct {
 
 func pkhash(pk []byte) []byte {
 	z := sha256.Sum256(pk)
-	return z[:16]
+	return z[:PKHashLength]
 }
 
 // Generate a new Ed25519 keypair
@@ -220,7 +223,6 @@ func MakePrivateKey(yml []byte, pw string) (*PrivateKey, error) {
 		return nil, fmt.Errorf("can't decode YAML:Verify: %s", err)
 	}
 
-	sk := &PrivateKey{}
 
 	// We take short passwords and extend them
 	pwb := sha512.Sum512([]byte(pw))
@@ -240,11 +242,24 @@ func MakePrivateKey(yml []byte, pw string) (*PrivateKey, error) {
 	}
 
 	// Everything works. Now, decode the key
-	sk.Sk = make([]byte, len(esk.Esk))
+	skb := make([]byte, len(esk.Esk))
 	for i := 0; i < len(esk.Esk); i++ {
-		sk.Sk[i] = esk.Esk[i] ^ xork[i]
+		skb[i] = esk.Esk[i] ^ xork[i]
 	}
 
+	edsk := Ed.PrivateKey(skb)
+	edpk := edsk.Public().(Ed.PublicKey)
+
+	pk := &PublicKey{
+		Pk:   []byte(edpk),
+		hash: pkhash([]byte(edpk)),
+	}
+	sk := &PrivateKey{
+		Sk: skb,
+		pk: pk,
+	}
+
+
 	return sk, nil
 }
 
diff --git a/sigtool.go b/sigtool.go
index 2ee2319..c21013b 100644
--- a/sigtool.go
+++ b/sigtool.go
@@ -306,6 +306,8 @@ Commands:
   generate, g      Generate a new Ed25519 keypair
   sign, s          Sign a file with a private key
   verify, v        Verify a signature against a file and a public key
+  encrypt, e       Encrypt an input file to one or more recipients
+  decrypt, d       Decrypt a file with a private key
 `, Z, Z)
 
 	os.Stdout.Write([]byte(x))
diff --git a/version b/version
new file mode 100644
index 0000000..0ea3a94
--- /dev/null
+++ b/version
@@ -0,0 +1 @@
+0.2.0