1 files changed, 102 insertions, 0 deletions
diff --git a/src/pkg/crypto/openpgp/packet/symmetric_key_encrypted.go b/src/pkg/crypto/openpgp/packet/symmetric_key_encrypted.go
new file mode 100644
index 000000000..d9010f88a
--- /dev/null
+++ b/src/pkg/crypto/openpgp/packet/symmetric_key_encrypted.go
@@ -0,0 +1,102 @@
+// 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.
+
+package packet
+
+import (
+	"crypto/cipher"
+	"crypto/openpgp/error"
+	"crypto/openpgp/s2k"
+	"io"
+	"os"
+	"strconv"
+)
+
+// This is the largest session key that we'll support. Since no 512-bit cipher
+// has even been seriously used, this is comfortably large.
+const maxSessionKeySizeInBytes = 64
+
+// SymmetricKeyEncrypted represents a passphrase protected session key. See RFC
+// 4880, section 5.3.
+type SymmetricKeyEncrypted struct {
+	CipherFunc   CipherFunction
+	Encrypted    bool
+	Key          []byte // Empty unless Encrypted is false.
+	s2k          func(out, in []byte)
+	encryptedKey []byte
+}
+
+func (ske *SymmetricKeyEncrypted) parse(r io.Reader) (err os.Error) {
+	// RFC 4880, section 5.3.
+	var buf [2]byte
+	_, err = readFull(r, buf[:])
+	if err != nil {
+		return
+	}
+	if buf[0] != 4 {
+		return error.UnsupportedError("SymmetricKeyEncrypted version")
+	}
+	ske.CipherFunc = CipherFunction(buf[1])
+
+	if ske.CipherFunc.keySize() == 0 {
+		return error.UnsupportedError("unknown cipher: " + strconv.Itoa(int(buf[1])))
+	}
+
+	ske.s2k, err = s2k.Parse(r)
+	if err != nil {
+		return
+	}
+
+	encryptedKey := make([]byte, maxSessionKeySizeInBytes)
+	// The session key may follow. We just have to try and read to find
+	// out. If it exists then we limit it to maxSessionKeySizeInBytes.
+	n, err := readFull(r, encryptedKey)
+	if err != nil && err != io.ErrUnexpectedEOF {
+		return
+	}
+	err = nil
+	if n != 0 {
+		if n == maxSessionKeySizeInBytes {
+			return error.UnsupportedError("oversized encrypted session key")
+		}
+		ske.encryptedKey = encryptedKey[:n]
+	}
+
+	ske.Encrypted = true
+
+	return
+}
+
+// Decrypt attempts to decrypt an encrypted session key. If it returns nil,
+// ske.Key will contain the session key.
+func (ske *SymmetricKeyEncrypted) Decrypt(passphrase []byte) os.Error {
+	if !ske.Encrypted {
+		return nil
+	}
+
+	key := make([]byte, ske.CipherFunc.keySize())
+	ske.s2k(key, passphrase)
+
+	if len(ske.encryptedKey) == 0 {
+		ske.Key = key
+	} else {
+		// the IV is all zeros
+		iv := make([]byte, ske.CipherFunc.blockSize())
+		c := cipher.NewCFBDecrypter(ske.CipherFunc.new(key), iv)
+		c.XORKeyStream(ske.encryptedKey, ske.encryptedKey)
+		ske.CipherFunc = CipherFunction(ske.encryptedKey[0])
+		if ske.CipherFunc.blockSize() == 0 {
+			return error.UnsupportedError("unknown cipher: " + strconv.Itoa(int(ske.CipherFunc)))
+		}
+		ske.CipherFunc = CipherFunction(ske.encryptedKey[0])
+		ske.Key = ske.encryptedKey[1:]
+		if len(ske.Key)%ske.CipherFunc.blockSize() != 0 {
+			ske.Key = nil
+			return error.StructuralError("length of decrypted key not a multiple of block size")
+		}
+	}
+
+	ske.Encrypted = false
+	return nil
+}