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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This package implements the various OpenPGP string-to-key transforms as
// specified in RFC 4800 section 3.7.1.
package s2k
import (
"crypto/md5"
"crypto/openpgp/error"
"crypto/ripemd160"
"crypto/sha1"
"crypto/sha256"
"crypto/sha512"
"hash"
"io"
"os"
)
// Simple writes to out the result of computing the Simple S2K function (RFC
// 4880, section 3.7.1.1) using the given hash and input passphrase.
func Simple(out []byte, h hash.Hash, in []byte) {
Salted(out, h, in, nil)
}
var zero [1]byte
// Salted writes to out the result of computing the Salted S2K function (RFC
// 4880, section 3.7.1.2) using the given hash, input passphrase and salt.
func Salted(out []byte, h hash.Hash, in []byte, salt []byte) {
done := 0
for i := 0; done < len(out); i++ {
h.Reset()
for j := 0; j < i; j++ {
h.Write(zero[:])
}
h.Write(salt)
h.Write(in)
n := copy(out[done:], h.Sum())
done += n
}
}
// Iterated writes to out the result of computing the Iterated and Salted S2K
// function (RFC 4880, section 3.7.1.3) using the given hash, input passphrase,
// salt and iteration count.
func Iterated(out []byte, h hash.Hash, in []byte, salt []byte, count int) {
combined := make([]byte, len(in)+len(salt))
copy(combined, salt)
copy(combined[len(salt):], in)
if count < len(combined) {
count = len(combined)
}
done := 0
for i := 0; done < len(out); i++ {
h.Reset()
for j := 0; j < i; j++ {
h.Write(zero[:])
}
written := 0
for written < count {
if written+len(combined) > count {
todo := count - written
h.Write(combined[:todo])
written = count
} else {
h.Write(combined)
written += len(combined)
}
}
n := copy(out[done:], h.Sum())
done += n
}
}
// Parse reads a binary specification for a string-to-key transformation from r
// and returns a function which performs that transform.
func Parse(r io.Reader) (f func(out, in []byte), err os.Error) {
var buf [9]byte
_, err = io.ReadFull(r, buf[:2])
if err != nil {
return
}
h := hashFuncFromType(buf[1])
if h == nil {
return nil, error.UnsupportedError("hash for S2K function")
}
switch buf[0] {
case 1:
f := func(out, in []byte) {
Simple(out, h, in)
}
return f, nil
case 2:
_, err := io.ReadFull(r, buf[:8])
if err != nil {
return
}
f := func(out, in []byte) {
Salted(out, h, in, buf[:8])
}
return f, nil
case 3:
_, err := io.ReadFull(r, buf[:9])
if err != nil {
return
}
count := (16 + int(buf[8]&15)) << (uint32(buf[8]>>4) + 6)
f := func(out, in []byte) {
Iterated(out, h, in, buf[:8], count)
}
return f, nil
}
return nil, error.UnsupportedError("S2K function")
}
// hashFuncFromType returns a hash.Hash which corresponds to the given hash
// type byte. See RFC 4880, section 9.4.
func hashFuncFromType(hashType byte) hash.Hash {
switch hashType {
case 1:
return md5.New()
case 2:
return sha1.New()
case 3:
return ripemd160.New()
case 8:
return sha256.New()
case 9:
return sha512.New384()
case 10:
return sha512.New()
case 11:
return sha256.New224()
}
return nil
}
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