1 files changed, 273 insertions, 0 deletions
diff --git a/libgo/go/crypto/rsa/pkcs1v15.go b/libgo/go/crypto/rsa/pkcs1v15.go
new file mode 100644
index 000000000..714046250
--- /dev/null
+++ b/libgo/go/crypto/rsa/pkcs1v15.go
@@ -0,0 +1,273 @@
+// Copyright 2009 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 rsa
+
+import (
+	"big"
+	"crypto/subtle"
+	"io"
+	"os"
+)
+
+// This file implements encryption and decryption using PKCS#1 v1.5 padding.
+
+// EncryptPKCS1v15 encrypts the given message with RSA and the padding scheme from PKCS#1 v1.5.
+// The message must be no longer than the length of the public modulus minus 11 bytes.
+// WARNING: use of this function to encrypt plaintexts other than session keys
+// is dangerous. Use RSA OAEP in new protocols.
+func EncryptPKCS1v15(rand io.Reader, pub *PublicKey, msg []byte) (out []byte, err os.Error) {
+	k := (pub.N.BitLen() + 7) / 8
+	if len(msg) > k-11 {
+		err = MessageTooLongError{}
+		return
+	}
+
+	// EM = 0x02 || PS || 0x00 || M
+	em := make([]byte, k-1)
+	em[0] = 2
+	ps, mm := em[1:len(em)-len(msg)-1], em[len(em)-len(msg):]
+	err = nonZeroRandomBytes(ps, rand)
+	if err != nil {
+		return
+	}
+	em[len(em)-len(msg)-1] = 0
+	copy(mm, msg)
+
+	m := new(big.Int).SetBytes(em)
+	c := encrypt(new(big.Int), pub, m)
+	out = c.Bytes()
+	return
+}
+
+// DecryptPKCS1v15 decrypts a plaintext using RSA and the padding scheme from PKCS#1 v1.5.
+// If rand != nil, it uses RSA blinding to avoid timing side-channel attacks.
+func DecryptPKCS1v15(rand io.Reader, priv *PrivateKey, ciphertext []byte) (out []byte, err os.Error) {
+	valid, out, err := decryptPKCS1v15(rand, priv, ciphertext)
+	if err == nil && valid == 0 {
+		err = DecryptionError{}
+	}
+
+	return
+}
+
+// DecryptPKCS1v15SessionKey decrypts a session key using RSA and the padding scheme from PKCS#1 v1.5.
+// If rand != nil, it uses RSA blinding to avoid timing side-channel attacks.
+// It returns an error if the ciphertext is the wrong length or if the
+// ciphertext is greater than the public modulus. Otherwise, no error is
+// returned. If the padding is valid, the resulting plaintext message is copied
+// into key. Otherwise, key is unchanged. These alternatives occur in constant
+// time. It is intended that the user of this function generate a random
+// session key beforehand and continue the protocol with the resulting value.
+// This will remove any possibility that an attacker can learn any information
+// about the plaintext.
+// See ``Chosen Ciphertext Attacks Against Protocols Based on the RSA
+// Encryption Standard PKCS #1'', Daniel Bleichenbacher, Advances in Cryptology
+// (Crypto '98),
+func DecryptPKCS1v15SessionKey(rand io.Reader, priv *PrivateKey, ciphertext []byte, key []byte) (err os.Error) {
+	k := (priv.N.BitLen() + 7) / 8
+	if k-(len(key)+3+8) < 0 {
+		err = DecryptionError{}
+		return
+	}
+
+	valid, msg, err := decryptPKCS1v15(rand, priv, ciphertext)
+	if err != nil {
+		return
+	}
+
+	valid &= subtle.ConstantTimeEq(int32(len(msg)), int32(len(key)))
+	subtle.ConstantTimeCopy(valid, key, msg)
+	return
+}
+
+func decryptPKCS1v15(rand io.Reader, priv *PrivateKey, ciphertext []byte) (valid int, msg []byte, err os.Error) {
+	k := (priv.N.BitLen() + 7) / 8
+	if k < 11 {
+		err = DecryptionError{}
+		return
+	}
+
+	c := new(big.Int).SetBytes(ciphertext)
+	m, err := decrypt(rand, priv, c)
+	if err != nil {
+		return
+	}
+
+	em := leftPad(m.Bytes(), k)
+	firstByteIsZero := subtle.ConstantTimeByteEq(em[0], 0)
+	secondByteIsTwo := subtle.ConstantTimeByteEq(em[1], 2)
+
+	// The remainder of the plaintext must be a string of non-zero random
+	// octets, followed by a 0, followed by the message.
+	//   lookingForIndex: 1 iff we are still looking for the zero.
+	//   index: the offset of the first zero byte.
+	var lookingForIndex, index int
+	lookingForIndex = 1
+
+	for i := 2; i < len(em); i++ {
+		equals0 := subtle.ConstantTimeByteEq(em[i], 0)
+		index = subtle.ConstantTimeSelect(lookingForIndex&equals0, i, index)
+		lookingForIndex = subtle.ConstantTimeSelect(equals0, 0, lookingForIndex)
+	}
+
+	valid = firstByteIsZero & secondByteIsTwo & (^lookingForIndex & 1)
+	msg = em[index+1:]
+	return
+}
+
+// nonZeroRandomBytes fills the given slice with non-zero random octets.
+func nonZeroRandomBytes(s []byte, rand io.Reader) (err os.Error) {
+	_, err = io.ReadFull(rand, s)
+	if err != nil {
+		return
+	}
+
+	for i := 0; i < len(s); i++ {
+		for s[i] == 0 {
+			_, err = rand.Read(s[i : i+1])
+			if err != nil {
+				return
+			}
+			// In tests, the PRNG may return all zeros so we do
+			// this to break the loop.
+			s[i] ^= 0x42
+		}
+	}
+
+	return
+}
+
+// Due to the design of PKCS#1 v1.5, we need to know the exact hash function in
+// use. A generic hash.Hash will not do.
+type PKCS1v15Hash int
+
+const (
+	HashMD5 PKCS1v15Hash = iota
+	HashSHA1
+	HashSHA256
+	HashSHA384
+	HashSHA512
+	HashMD5SHA1 // combined MD5 and SHA1 hash used for RSA signing in TLS.
+)
+
+// These are ASN1 DER structures:
+//   DigestInfo ::= SEQUENCE {
+//     digestAlgorithm AlgorithmIdentifier,
+//     digest OCTET STRING
+//   }
+// For performance, we don't use the generic ASN1 encoder. Rather, we
+// precompute a prefix of the digest value that makes a valid ASN1 DER string
+// with the correct contents.
+var hashPrefixes = [][]byte{
+	// HashMD5
+	{0x30, 0x20, 0x30, 0x0c, 0x06, 0x08, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x02, 0x05, 0x05, 0x00, 0x04, 0x10},
+	// HashSHA1
+	{0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2b, 0x0e, 0x03, 0x02, 0x1a, 0x05, 0x00, 0x04, 0x14},
+	// HashSHA256
+	{0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20},
+	// HashSHA384
+	{0x30, 0x41, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02, 0x05, 0x00, 0x04, 0x30},
+	// HashSHA512
+	{0x30, 0x51, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03, 0x05, 0x00, 0x04, 0x40},
+	// HashMD5SHA1
+	{}, // A special TLS case which doesn't use an ASN1 prefix.
+}
+
+// SignPKCS1v15 calcuates the signature of hashed using RSASSA-PSS-SIGN from RSA PKCS#1 v1.5.
+// Note that hashed must be the result of hashing the input message using the
+// given hash function.
+func SignPKCS1v15(rand io.Reader, priv *PrivateKey, hash PKCS1v15Hash, hashed []byte) (s []byte, err os.Error) {
+	hashLen, prefix, err := pkcs1v15HashInfo(hash, len(hashed))
+	if err != nil {
+		return
+	}
+
+	tLen := len(prefix) + hashLen
+	k := (priv.N.BitLen() + 7) / 8
+	if k < tLen+11 {
+		return nil, MessageTooLongError{}
+	}
+
+	// EM = 0x00 || 0x01 || PS || 0x00 || T
+	em := make([]byte, k)
+	em[1] = 1
+	for i := 2; i < k-tLen-1; i++ {
+		em[i] = 0xff
+	}
+	copy(em[k-tLen:k-hashLen], prefix)
+	copy(em[k-hashLen:k], hashed)
+
+	m := new(big.Int).SetBytes(em)
+	c, err := decrypt(rand, priv, m)
+	if err == nil {
+		s = c.Bytes()
+	}
+	return
+}
+
+// VerifyPKCS1v15 verifies an RSA PKCS#1 v1.5 signature.
+// hashed is the result of hashing the input message using the given hash
+// function and sig is the signature. A valid signature is indicated by
+// returning a nil error.
+func VerifyPKCS1v15(pub *PublicKey, hash PKCS1v15Hash, hashed []byte, sig []byte) (err os.Error) {
+	hashLen, prefix, err := pkcs1v15HashInfo(hash, len(hashed))
+	if err != nil {
+		return
+	}
+
+	tLen := len(prefix) + hashLen
+	k := (pub.N.BitLen() + 7) / 8
+	if k < tLen+11 {
+		err = VerificationError{}
+		return
+	}
+
+	c := new(big.Int).SetBytes(sig)
+	m := encrypt(new(big.Int), pub, c)
+	em := leftPad(m.Bytes(), k)
+	// EM = 0x00 || 0x01 || PS || 0x00 || T
+
+	ok := subtle.ConstantTimeByteEq(em[0], 0)
+	ok &= subtle.ConstantTimeByteEq(em[1], 1)
+	ok &= subtle.ConstantTimeCompare(em[k-hashLen:k], hashed)
+	ok &= subtle.ConstantTimeCompare(em[k-tLen:k-hashLen], prefix)
+	ok &= subtle.ConstantTimeByteEq(em[k-tLen-1], 0)
+
+	for i := 2; i < k-tLen-1; i++ {
+		ok &= subtle.ConstantTimeByteEq(em[i], 0xff)
+	}
+
+	if ok != 1 {
+		return VerificationError{}
+	}
+
+	return nil
+}
+
+func pkcs1v15HashInfo(hash PKCS1v15Hash, inLen int) (hashLen int, prefix []byte, err os.Error) {
+	switch hash {
+	case HashMD5:
+		hashLen = 16
+	case HashSHA1:
+		hashLen = 20
+	case HashSHA256:
+		hashLen = 32
+	case HashSHA384:
+		hashLen = 48
+	case HashSHA512:
+		hashLen = 64
+	case HashMD5SHA1:
+		hashLen = 36
+	default:
+		return 0, nil, os.ErrorString("unknown hash function")
+	}
+
+	if inLen != hashLen {
+		return 0, nil, os.ErrorString("input must be hashed message")
+	}
+
+	prefix = hashPrefixes[int(hash)]
+	return
+}