crypto/rsa: implement PSS signatures.
This change contains an implementation of the RSASSA-PSS signature
algorithm described in RFC 3447.
R=agl, agl
CC=gobot, golang-dev, r
https://golang.org/cl/9438043
diff --git a/src/pkg/crypto/rsa/pss.go b/src/pkg/crypto/rsa/pss.go
new file mode 100644
index 0000000..f9abec3
--- /dev/null
+++ b/src/pkg/crypto/rsa/pss.go
@@ -0,0 +1,282 @@
+// Copyright 2013 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
+
+// This file implementes the PSS signature scheme [1].
+//
+// [1] http://www.rsa.com/rsalabs/pkcs/files/h11300-wp-pkcs-1v2-2-rsa-cryptography-standard.pdf
+
+import (
+ "bytes"
+ "crypto"
+ "errors"
+ "hash"
+ "io"
+ "math/big"
+)
+
+func emsaPSSEncode(mHash []byte, emBits int, salt []byte, hash hash.Hash) ([]byte, error) {
+ // See [1], section 9.1.1
+ hLen := hash.Size()
+ sLen := len(salt)
+ emLen := (emBits + 7) / 8
+
+ // 1. If the length of M is greater than the input limitation for the
+ // hash function (2^61 - 1 octets for SHA-1), output "message too
+ // long" and stop.
+ //
+ // 2. Let mHash = Hash(M), an octet string of length hLen.
+
+ if len(mHash) != hLen {
+ return nil, errors.New("crypto/rsa: input must be hashed message")
+ }
+
+ // 3. If emLen < hLen + sLen + 2, output "encoding error" and stop.
+
+ if emLen < hLen+sLen+2 {
+ return nil, errors.New("crypto/rsa: encoding error")
+ }
+
+ em := make([]byte, emLen)
+ db := em[:emLen-sLen-hLen-2+1+sLen]
+ h := em[emLen-sLen-hLen-2+1+sLen : emLen-1]
+
+ // 4. Generate a random octet string salt of length sLen; if sLen = 0,
+ // then salt is the empty string.
+ //
+ // 5. Let
+ // M' = (0x)00 00 00 00 00 00 00 00 || mHash || salt;
+ //
+ // M' is an octet string of length 8 + hLen + sLen with eight
+ // initial zero octets.
+ //
+ // 6. Let H = Hash(M'), an octet string of length hLen.
+
+ var prefix [8]byte
+
+ hash.Write(prefix[:])
+ hash.Write(mHash)
+ hash.Write(salt)
+
+ h = hash.Sum(h[:0])
+ hash.Reset()
+
+ // 7. Generate an octet string PS consisting of emLen - sLen - hLen - 2
+ // zero octets. The length of PS may be 0.
+ //
+ // 8. Let DB = PS || 0x01 || salt; DB is an octet string of length
+ // emLen - hLen - 1.
+
+ db[emLen-sLen-hLen-2] = 0x01
+ copy(db[emLen-sLen-hLen-1:], salt)
+
+ // 9. Let dbMask = MGF(H, emLen - hLen - 1).
+ //
+ // 10. Let maskedDB = DB \xor dbMask.
+
+ mgf1XOR(db, hash, h)
+
+ // 11. Set the leftmost 8 * emLen - emBits bits of the leftmost octet in
+ // maskedDB to zero.
+
+ db[0] &= (0xFF >> uint(8*emLen-emBits))
+
+ // 12. Let EM = maskedDB || H || 0xbc.
+ em[emLen-1] = 0xBC
+
+ // 13. Output EM.
+ return em, nil
+}
+
+func emsaPSSVerify(mHash, em []byte, emBits, sLen int, hash hash.Hash) error {
+ // 1. If the length of M is greater than the input limitation for the
+ // hash function (2^61 - 1 octets for SHA-1), output "inconsistent"
+ // and stop.
+ //
+ // 2. Let mHash = Hash(M), an octet string of length hLen.
+ hLen := hash.Size()
+ if hLen != len(mHash) {
+ return ErrVerification
+ }
+
+ // 3. If emLen < hLen + sLen + 2, output "inconsistent" and stop.
+ emLen := (emBits + 7) / 8
+ if emLen < hLen+sLen+2 {
+ return ErrVerification
+ }
+
+ // 4. If the rightmost octet of EM does not have hexadecimal value
+ // 0xbc, output "inconsistent" and stop.
+ if em[len(em)-1] != 0xBC {
+ return ErrVerification
+ }
+
+ // 5. Let maskedDB be the leftmost emLen - hLen - 1 octets of EM, and
+ // let H be the next hLen octets.
+ db := em[:emLen-hLen-1]
+ h := em[emLen-hLen-1 : len(em)-1]
+
+ // 6. If the leftmost 8 * emLen - emBits bits of the leftmost octet in
+ // maskedDB are not all equal to zero, output "inconsistent" and
+ // stop.
+ if em[0]&(0xFF<<uint(8-(8*emLen-emBits))) != 0 {
+ return ErrVerification
+ }
+
+ // 7. Let dbMask = MGF(H, emLen - hLen - 1).
+ //
+ // 8. Let DB = maskedDB \xor dbMask.
+ mgf1XOR(db, hash, h)
+
+ // 9. Set the leftmost 8 * emLen - emBits bits of the leftmost octet in DB
+ // to zero.
+ db[0] &= (0xFF >> uint(8*emLen-emBits))
+
+ if sLen == PSSSaltLengthAuto {
+ FindSaltLength:
+ for sLen = emLen - (hLen + 2); sLen >= 0; sLen-- {
+ switch db[emLen-hLen-sLen-2] {
+ case 1:
+ break FindSaltLength
+ case 0:
+ continue
+ default:
+ return ErrVerification
+ }
+ }
+ if sLen < 0 {
+ return ErrVerification
+ }
+ } else {
+ // 10. If the emLen - hLen - sLen - 2 leftmost octets of DB are not zero
+ // or if the octet at position emLen - hLen - sLen - 1 (the leftmost
+ // position is "position 1") does not have hexadecimal value 0x01,
+ // output "inconsistent" and stop.
+ for _, e := range db[:emLen-hLen-sLen-2] {
+ if e != 0x00 {
+ return ErrVerification
+ }
+ }
+ if db[emLen-hLen-sLen-2] != 0x01 {
+ return ErrVerification
+ }
+ }
+
+ // 11. Let salt be the last sLen octets of DB.
+ salt := db[len(db)-sLen:]
+
+ // 12. Let
+ // M' = (0x)00 00 00 00 00 00 00 00 || mHash || salt ;
+ // M' is an octet string of length 8 + hLen + sLen with eight
+ // initial zero octets.
+ //
+ // 13. Let H' = Hash(M'), an octet string of length hLen.
+ var prefix [8]byte
+ hash.Write(prefix[:])
+ hash.Write(mHash)
+ hash.Write(salt)
+
+ h0 := hash.Sum(nil)
+
+ // 14. If H = H', output "consistent." Otherwise, output "inconsistent."
+ if !bytes.Equal(h0, h) {
+ return ErrVerification
+ }
+ return nil
+}
+
+// signPSSWithSalt calculates the signature of hashed using PSS [1] with specified salt.
+// Note that hashed must be the result of hashing the input message using the
+// given hash funcion. salt is a random sequence of bytes whose length will be
+// later used to verify the signature.
+func signPSSWithSalt(rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed, salt []byte) (s []byte, err error) {
+ nBits := priv.N.BitLen()
+ em, err := emsaPSSEncode(hashed, nBits-1, salt, hash.New())
+ if err != nil {
+ return
+ }
+ m := new(big.Int).SetBytes(em)
+ c, err := decrypt(rand, priv, m)
+ if err != nil {
+ return
+ }
+ s = make([]byte, (nBits+7)/8)
+ copyWithLeftPad(s, c.Bytes())
+ return
+}
+
+const (
+ // PSSSaltLengthAuto causes the salt in a PSS signature to be as large
+ // as possible when signing, and to be auto-detected when verifying.
+ PSSSaltLengthAuto = 0
+ // PSSSaltLengthEqualsHash causes the salt length to equal the length
+ // of the hash used in the signature.
+ PSSSaltLengthEqualsHash = -1
+)
+
+// PSSOptions contains options for creating and verifying PSS signatures.
+type PSSOptions struct {
+ // SaltLength controls the length of the salt used in the PSS
+ // signature. It can either be a number of bytes, or one of the special
+ // PSSSaltLength constants.
+ SaltLength int
+}
+
+func (opts *PSSOptions) saltLength() int {
+ if opts == nil {
+ return PSSSaltLengthAuto
+ }
+ return opts.SaltLength
+}
+
+// SignPSS calculates the signature of hashed using RSASSA-PSS [1].
+// Note that hashed must be the result of hashing the input message using the
+// given hash funcion. The opts argument may be nil, in which case sensible
+// defaults are used.
+func SignPSS(rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []byte, opts *PSSOptions) (s []byte, err error) {
+ saltLength := opts.saltLength()
+ switch saltLength {
+ case PSSSaltLengthAuto:
+ saltLength = (priv.N.BitLen()+7)/8 - 2 - hash.Size()
+ case PSSSaltLengthEqualsHash:
+ saltLength = hash.Size()
+ }
+
+ salt := make([]byte, saltLength)
+ if _, err = io.ReadFull(rand, salt); err != nil {
+ return
+ }
+ return signPSSWithSalt(rand, priv, hash, hashed, salt)
+}
+
+// VerifyPSS verifies a PSS 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. The opts argument may be nil, in which case sensible
+// defaults are used.
+func VerifyPSS(pub *PublicKey, hash crypto.Hash, hashed []byte, sig []byte, opts *PSSOptions) error {
+ return verifyPSS(pub, hash, hashed, sig, opts.saltLength())
+}
+
+// verifyPSS verifies a PSS signature with the given salt length.
+func verifyPSS(pub *PublicKey, hash crypto.Hash, hashed []byte, sig []byte, saltLen int) error {
+ nBits := pub.N.BitLen()
+ if len(sig) != (nBits+7)/8 {
+ return ErrVerification
+ }
+ s := new(big.Int).SetBytes(sig)
+ m := encrypt(new(big.Int), pub, s)
+ emBits := nBits - 1
+ emLen := (emBits + 7) / 8
+ if emLen < len(m.Bytes()) {
+ return ErrVerification
+ }
+ em := make([]byte, emLen)
+ copyWithLeftPad(em, m.Bytes())
+ if saltLen == PSSSaltLengthEqualsHash {
+ saltLen = hash.Size()
+ }
+ return emsaPSSVerify(hashed, em, emBits, saltLen, hash.New())
+}
diff --git a/src/pkg/crypto/rsa/pss_test.go b/src/pkg/crypto/rsa/pss_test.go
new file mode 100644
index 0000000..32e6fc3
--- /dev/null
+++ b/src/pkg/crypto/rsa/pss_test.go
@@ -0,0 +1,249 @@
+// Copyright 2013 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 (
+ "bufio"
+ "bytes"
+ "compress/bzip2"
+ "crypto"
+ _ "crypto/md5"
+ "crypto/rand"
+ "crypto/sha1"
+ _ "crypto/sha256"
+ "encoding/hex"
+ "math/big"
+ "os"
+ "strconv"
+ "strings"
+ "testing"
+)
+
+func TestEMSAPSS(t *testing.T) {
+ // Test vector in file pss-int.txt from: ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1-vec.zip
+ msg := []byte{
+ 0x85, 0x9e, 0xef, 0x2f, 0xd7, 0x8a, 0xca, 0x00, 0x30, 0x8b,
+ 0xdc, 0x47, 0x11, 0x93, 0xbf, 0x55, 0xbf, 0x9d, 0x78, 0xdb,
+ 0x8f, 0x8a, 0x67, 0x2b, 0x48, 0x46, 0x34, 0xf3, 0xc9, 0xc2,
+ 0x6e, 0x64, 0x78, 0xae, 0x10, 0x26, 0x0f, 0xe0, 0xdd, 0x8c,
+ 0x08, 0x2e, 0x53, 0xa5, 0x29, 0x3a, 0xf2, 0x17, 0x3c, 0xd5,
+ 0x0c, 0x6d, 0x5d, 0x35, 0x4f, 0xeb, 0xf7, 0x8b, 0x26, 0x02,
+ 0x1c, 0x25, 0xc0, 0x27, 0x12, 0xe7, 0x8c, 0xd4, 0x69, 0x4c,
+ 0x9f, 0x46, 0x97, 0x77, 0xe4, 0x51, 0xe7, 0xf8, 0xe9, 0xe0,
+ 0x4c, 0xd3, 0x73, 0x9c, 0x6b, 0xbf, 0xed, 0xae, 0x48, 0x7f,
+ 0xb5, 0x56, 0x44, 0xe9, 0xca, 0x74, 0xff, 0x77, 0xa5, 0x3c,
+ 0xb7, 0x29, 0x80, 0x2f, 0x6e, 0xd4, 0xa5, 0xff, 0xa8, 0xba,
+ 0x15, 0x98, 0x90, 0xfc,
+ }
+ salt := []byte{
+ 0xe3, 0xb5, 0xd5, 0xd0, 0x02, 0xc1, 0xbc, 0xe5, 0x0c, 0x2b,
+ 0x65, 0xef, 0x88, 0xa1, 0x88, 0xd8, 0x3b, 0xce, 0x7e, 0x61,
+ }
+ expected := []byte{
+ 0x66, 0xe4, 0x67, 0x2e, 0x83, 0x6a, 0xd1, 0x21, 0xba, 0x24,
+ 0x4b, 0xed, 0x65, 0x76, 0xb8, 0x67, 0xd9, 0xa4, 0x47, 0xc2,
+ 0x8a, 0x6e, 0x66, 0xa5, 0xb8, 0x7d, 0xee, 0x7f, 0xbc, 0x7e,
+ 0x65, 0xaf, 0x50, 0x57, 0xf8, 0x6f, 0xae, 0x89, 0x84, 0xd9,
+ 0xba, 0x7f, 0x96, 0x9a, 0xd6, 0xfe, 0x02, 0xa4, 0xd7, 0x5f,
+ 0x74, 0x45, 0xfe, 0xfd, 0xd8, 0x5b, 0x6d, 0x3a, 0x47, 0x7c,
+ 0x28, 0xd2, 0x4b, 0xa1, 0xe3, 0x75, 0x6f, 0x79, 0x2d, 0xd1,
+ 0xdc, 0xe8, 0xca, 0x94, 0x44, 0x0e, 0xcb, 0x52, 0x79, 0xec,
+ 0xd3, 0x18, 0x3a, 0x31, 0x1f, 0xc8, 0x96, 0xda, 0x1c, 0xb3,
+ 0x93, 0x11, 0xaf, 0x37, 0xea, 0x4a, 0x75, 0xe2, 0x4b, 0xdb,
+ 0xfd, 0x5c, 0x1d, 0xa0, 0xde, 0x7c, 0xec, 0xdf, 0x1a, 0x89,
+ 0x6f, 0x9d, 0x8b, 0xc8, 0x16, 0xd9, 0x7c, 0xd7, 0xa2, 0xc4,
+ 0x3b, 0xad, 0x54, 0x6f, 0xbe, 0x8c, 0xfe, 0xbc,
+ }
+
+ hash := sha1.New()
+ hash.Write(msg)
+ hashed := hash.Sum(nil)
+
+ encoded, err := emsaPSSEncode(hashed, 1023, salt, sha1.New())
+ if err != nil {
+ t.Errorf("Error from emsaPSSEncode: %s\n", err)
+ }
+ if !bytes.Equal(encoded, expected) {
+ t.Errorf("Bad encoding. got %x, want %x", encoded, expected)
+ }
+
+ if err = emsaPSSVerify(hashed, encoded, 1023, len(salt), sha1.New()); err != nil {
+ t.Errorf("Bad verification: %s", err)
+ }
+}
+
+// TestPSSGolden tests all the test vectors in pss-vect.txt from
+// ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1-vec.zip
+func TestPSSGolden(t *testing.T) {
+ inFile, err := os.Open("testdata/pss-vect.txt.bz2")
+ if err != nil {
+ t.Fatalf("Failed to open input file: %s", err)
+ }
+ defer inFile.Close()
+
+ // The pss-vect.txt file contains RSA keys and then a series of
+ // signatures. A goroutine is used to preprocess the input by merging
+ // lines, removing spaces in hex values and identifying the start of
+ // new keys and signature blocks.
+ const newKeyMarker = "START NEW KEY"
+ const newSignatureMarker = "START NEW SIGNATURE"
+
+ values := make(chan string)
+
+ go func() {
+ defer close(values)
+ scanner := bufio.NewScanner(bzip2.NewReader(inFile))
+ var partialValue string
+ lastWasValue := true
+
+ for scanner.Scan() {
+ line := scanner.Text()
+ switch {
+ case len(line) == 0:
+ if len(partialValue) > 0 {
+ values <- strings.Replace(partialValue, " ", "", -1)
+ partialValue = ""
+ lastWasValue = true
+ }
+ continue
+ case strings.HasPrefix(line, "# ======") && lastWasValue:
+ values <- newKeyMarker
+ lastWasValue = false
+ case strings.HasPrefix(line, "# ------") && lastWasValue:
+ values <- newSignatureMarker
+ lastWasValue = false
+ case strings.HasPrefix(line, "#"):
+ continue
+ default:
+ partialValue += line
+ }
+ }
+ if err := scanner.Err(); err != nil {
+ panic(err)
+ }
+ }()
+
+ var key *PublicKey
+ var hashed []byte
+ hash := crypto.SHA1
+ h := hash.New()
+ opts := &PSSOptions{
+ SaltLength: PSSSaltLengthEqualsHash,
+ }
+
+ for marker := range values {
+ switch marker {
+ case newKeyMarker:
+ key = new(PublicKey)
+ nHex, ok := <-values
+ if !ok {
+ continue
+ }
+ key.N = bigFromHex(nHex)
+ key.E = intFromHex(<-values)
+ // We don't care for d, p, q, dP, dQ or qInv.
+ for i := 0; i < 6; i++ {
+ <-values
+ }
+ case newSignatureMarker:
+ msg := fromHex(<-values)
+ <-values // skip salt
+ sig := fromHex(<-values)
+
+ h.Reset()
+ h.Write(msg)
+ hashed = h.Sum(hashed[:0])
+
+ if err := VerifyPSS(key, hash, hashed, sig, opts); err != nil {
+ t.Error(err)
+ }
+ default:
+ t.Fatalf("unknown marker: " + marker)
+ }
+ }
+}
+
+// TestPSSOpenSSL ensures that we can verify a PSS signature from OpenSSL with
+// the default options. OpenSSL sets the salt length to be maximal.
+func TestPSSOpenSSL(t *testing.T) {
+ hash := crypto.SHA256
+ h := hash.New()
+ h.Write([]byte("testing"))
+ hashed := h.Sum(nil)
+
+ // Generated with `echo -n testing | openssl dgst -sign key.pem -sigopt rsa_padding_mode:pss -sha256 > sig`
+ sig := []byte{
+ 0x95, 0x59, 0x6f, 0xd3, 0x10, 0xa2, 0xe7, 0xa2, 0x92, 0x9d,
+ 0x4a, 0x07, 0x2e, 0x2b, 0x27, 0xcc, 0x06, 0xc2, 0x87, 0x2c,
+ 0x52, 0xf0, 0x4a, 0xcc, 0x05, 0x94, 0xf2, 0xc3, 0x2e, 0x20,
+ 0xd7, 0x3e, 0x66, 0x62, 0xb5, 0x95, 0x2b, 0xa3, 0x93, 0x9a,
+ 0x66, 0x64, 0x25, 0xe0, 0x74, 0x66, 0x8c, 0x3e, 0x92, 0xeb,
+ 0xc6, 0xe6, 0xc0, 0x44, 0xf3, 0xb4, 0xb4, 0x2e, 0x8c, 0x66,
+ 0x0a, 0x37, 0x9c, 0x69,
+ }
+
+ if err := VerifyPSS(&rsaPrivateKey.PublicKey, hash, hashed, sig, nil); err != nil {
+ t.Error(err)
+ }
+}
+
+func TestPSSSigning(t *testing.T) {
+ var saltLengthCombinations = []struct {
+ signSaltLength, verifySaltLength int
+ good bool
+ }{
+ {PSSSaltLengthAuto, PSSSaltLengthAuto, true},
+ {PSSSaltLengthEqualsHash, PSSSaltLengthAuto, true},
+ {PSSSaltLengthEqualsHash, PSSSaltLengthEqualsHash, true},
+ {PSSSaltLengthEqualsHash, 8, false},
+ {PSSSaltLengthAuto, PSSSaltLengthEqualsHash, false},
+ {8, 8, true},
+ }
+
+ hash := crypto.MD5
+ h := hash.New()
+ h.Write([]byte("testing"))
+ hashed := h.Sum(nil)
+ var opts PSSOptions
+
+ for i, test := range saltLengthCombinations {
+ opts.SaltLength = test.signSaltLength
+ sig, err := SignPSS(rand.Reader, rsaPrivateKey, hash, hashed, &opts)
+ if err != nil {
+ t.Errorf("#%d: error while signing: %s", i, err)
+ continue
+ }
+
+ opts.SaltLength = test.verifySaltLength
+ err = VerifyPSS(&rsaPrivateKey.PublicKey, hash, hashed, sig, &opts)
+ if (err == nil) != test.good {
+ t.Errorf("#%d: bad result, wanted: %t, got: %s", i, test.good, err)
+ }
+ }
+}
+
+func bigFromHex(hex string) *big.Int {
+ n, ok := new(big.Int).SetString(hex, 16)
+ if !ok {
+ panic("bad hex: " + hex)
+ }
+ return n
+}
+
+func intFromHex(hex string) int {
+ i, err := strconv.ParseInt(hex, 16, 32)
+ if err != nil {
+ panic(err)
+ }
+ return int(i)
+}
+
+func fromHex(hexStr string) []byte {
+ s, err := hex.DecodeString(hexStr)
+ if err != nil {
+ panic(err)
+ }
+ return s
+}
diff --git a/src/pkg/crypto/rsa/rsa_test.go b/src/pkg/crypto/rsa/rsa_test.go
index ffd96e6..cf193c6 100644
--- a/src/pkg/crypto/rsa/rsa_test.go
+++ b/src/pkg/crypto/rsa/rsa_test.go
@@ -120,8 +120,10 @@
}
func fromBase10(base10 string) *big.Int {
- i := new(big.Int)
- i.SetString(base10, 10)
+ i, ok := new(big.Int).SetString(base10, 10)
+ if !ok {
+ panic("bad number: " + base10)
+ }
return i
}
diff --git a/src/pkg/crypto/rsa/testdata/pss-vect.txt.bz2 b/src/pkg/crypto/rsa/testdata/pss-vect.txt.bz2
new file mode 100644
index 0000000..ad3da1a
--- /dev/null
+++ b/src/pkg/crypto/rsa/testdata/pss-vect.txt.bz2
Binary files differ
