--- /dev/null
+// 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 dsa implements the Digital Signature Algorithm, as defined in FIPS 186-3
+package dsa
+
+import (
+ "big"
+ "io"
+ "os"
+)
+
+// Parameters represents the domain parameters for a key. These parameters can
+// be shared across many keys. The bit length of Q must be a multiple of 8.
+type Parameters struct {
+ P, Q, G *big.Int
+}
+
+// PublicKey represents a DSA public key.
+type PublicKey struct {
+ Parameters
+ Y *big.Int
+}
+
+// PrivateKey represents a DSA private key.
+type PrivateKey struct {
+ PublicKey
+ X *big.Int
+}
+
+type invalidPublicKeyError int
+
+func (invalidPublicKeyError) String() string {
+ return "crypto/dsa: invalid public key"
+}
+
+// InvalidPublicKeyError results when a public key is not usable by this code.
+// FIPS is quite strict about the format of DSA keys, but other code may be
+// less so. Thus, when using keys which may have been generated by other code,
+// this error must be handled.
+var InvalidPublicKeyError = invalidPublicKeyError(0)
+
+// ParameterSizes is a enumeration of the acceptable bit lengths of the primes
+// in a set of DSA parameters. See FIPS 186-3, section 4.2.
+type ParameterSizes int
+
+const (
+ L1024N160 ParameterSizes = iota
+ L2048N224
+ L2048N256
+ L3072N256
+)
+
+// numMRTests is the number of Miller-Rabin primality tests that we perform. We
+// pick the largest recommended number from table C.1 of FIPS 186-3.
+const numMRTests = 64
+
+// GenerateParameters puts a random, valid set of DSA parameters into params.
+// This function takes many seconds, even on fast machines.
+func GenerateParameters(params *Parameters, rand io.Reader, sizes ParameterSizes) (err os.Error) {
+ // This function doesn't follow FIPS 186-3 exactly in that it doesn't
+ // use a verification seed to generate the primes. The verification
+ // seed doesn't appear to be exported or used by other code and
+ // omitting it makes the code cleaner.
+
+ var L, N int
+ switch sizes {
+ case L1024N160:
+ L = 1024
+ N = 160
+ case L2048N224:
+ L = 2048
+ N = 224
+ case L2048N256:
+ L = 2048
+ N = 256
+ case L3072N256:
+ L = 3072
+ N = 256
+ default:
+ return os.ErrorString("crypto/dsa: invalid ParameterSizes")
+ }
+
+ qBytes := make([]byte, N/8)
+ pBytes := make([]byte, L/8)
+
+ q := new(big.Int)
+ p := new(big.Int)
+ rem := new(big.Int)
+ one := new(big.Int)
+ one.SetInt64(1)
+
+GeneratePrimes:
+ for {
+ _, err = io.ReadFull(rand, qBytes)
+ if err != nil {
+ return
+ }
+
+ qBytes[len(qBytes)-1] |= 1
+ qBytes[0] |= 0x80
+ q.SetBytes(qBytes)
+
+ if !big.ProbablyPrime(q, numMRTests) {
+ continue
+ }
+
+ for i := 0; i < 4*L; i++ {
+ _, err = io.ReadFull(rand, pBytes)
+ if err != nil {
+ return
+ }
+
+ pBytes[len(pBytes)-1] |= 1
+ pBytes[0] |= 0x80
+
+ p.SetBytes(pBytes)
+ rem.Mod(p, q)
+ rem.Sub(rem, one)
+ p.Sub(p, rem)
+ if p.BitLen() < L {
+ continue
+ }
+
+ if !big.ProbablyPrime(p, numMRTests) {
+ continue
+ }
+
+ params.P = p
+ params.Q = q
+ break GeneratePrimes
+ }
+ }
+
+ h := new(big.Int)
+ h.SetInt64(2)
+ g := new(big.Int)
+
+ pm1 := new(big.Int).Sub(p, one)
+ e := new(big.Int).Div(pm1, q)
+
+ for {
+ g.Exp(h, e, p)
+ if g.Cmp(one) == 0 {
+ h.Add(h, one)
+ continue
+ }
+
+ params.G = g
+ return
+ }
+
+ panic("unreachable")
+}
+
+// GenerateKey generates a public&private key pair. The Parameters of the
+// PrivateKey must already be valid (see GenerateParameters).
+func GenerateKey(priv *PrivateKey, rand io.Reader) os.Error {
+ if priv.P == nil || priv.Q == nil || priv.G == nil {
+ return os.ErrorString("crypto/dsa: parameters not set up before generating key")
+ }
+
+ x := new(big.Int)
+ xBytes := make([]byte, priv.Q.BitLen()/8)
+
+ for {
+ _, err := io.ReadFull(rand, xBytes)
+ if err != nil {
+ return err
+ }
+ x.SetBytes(xBytes)
+ if x.Sign() != 0 && x.Cmp(priv.Q) < 0 {
+ break
+ }
+ }
+
+ priv.X = x
+ priv.Y = new(big.Int)
+ priv.Y.Exp(priv.G, x, priv.P)
+ return nil
+}
+
+// Sign signs an arbitrary length hash (which should be the result of hashing a
+// larger message) using the private key, priv. It returns the signature as a
+// pair of integers. The security of the private key depends on the entropy of
+// rand.
+func Sign(rand io.Reader, priv *PrivateKey, hash []byte) (r, s *big.Int, err os.Error) {
+ // FIPS 186-3, section 4.6
+
+ n := priv.Q.BitLen()
+ if n&7 != 0 {
+ err = InvalidPublicKeyError
+ return
+ }
+ n >>= 3
+
+ for {
+ k := new(big.Int)
+ buf := make([]byte, n)
+ for {
+ _, err = io.ReadFull(rand, buf)
+ if err != nil {
+ return
+ }
+ k.SetBytes(buf)
+ if k.Sign() > 0 && k.Cmp(priv.Q) < 0 {
+ break
+ }
+ }
+
+ kInv := new(big.Int).ModInverse(k, priv.Q)
+
+ r = new(big.Int).Exp(priv.G, k, priv.P)
+ r.Mod(r, priv.Q)
+
+ if r.Sign() == 0 {
+ continue
+ }
+
+ if n > len(hash) {
+ n = len(hash)
+ }
+ z := k.SetBytes(hash[:n])
+
+ s = new(big.Int).Mul(priv.X, r)
+ s.Add(s, z)
+ s.Mod(s, priv.Q)
+ s.Mul(s, kInv)
+ s.Mod(s, priv.Q)
+
+ if s.Sign() != 0 {
+ break
+ }
+ }
+
+ return
+}
+
+// Verify verifies the signature in r, s of hash using the public key, pub. It
+// returns true iff the signature is valid.
+func Verify(pub *PublicKey, hash []byte, r, s *big.Int) bool {
+ // FIPS 186-3, section 4.7
+
+ if r.Sign() < 1 || r.Cmp(pub.Q) >= 0 {
+ return false
+ }
+ if s.Sign() < 1 || s.Cmp(pub.Q) >= 0 {
+ return false
+ }
+
+ w := new(big.Int).ModInverse(s, pub.Q)
+
+ n := pub.Q.BitLen()
+ if n&7 != 0 {
+ return false
+ }
+ n >>= 3
+
+ if n > len(hash) {
+ n = len(hash)
+ }
+ z := new(big.Int).SetBytes(hash[:n])
+
+ u1 := new(big.Int).Mul(z, w)
+ u1.Mod(u1, pub.Q)
+ u2 := w.Mul(r, w)
+ u2.Mod(u2, pub.Q)
+ v := u1.Exp(pub.G, u1, pub.P)
+ u2.Exp(pub.Y, u2, pub.P)
+ v.Mul(v, u2)
+ v.Mod(v, pub.P)
+ v.Mod(v, pub.Q)
+
+ return v.Cmp(r) == 0
+}
--- /dev/null
+// 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 dsa
+
+import (
+ "big"
+ "crypto/rand"
+ "testing"
+)
+
+func testSignAndVerify(t *testing.T, i int, priv *PrivateKey) {
+ hashed := []byte("testing")
+ r, s, err := Sign(rand.Reader, priv, hashed)
+ if err != nil {
+ t.Errorf("%d: error signing: %s", i, err)
+ return
+ }
+
+ if !Verify(&priv.PublicKey, hashed, r, s) {
+ t.Errorf("%d: Verify failed", i)
+ }
+}
+
+func testParameterGeneration(t *testing.T, sizes ParameterSizes, L, N int) {
+ var priv PrivateKey
+ params := &priv.Parameters
+
+ err := GenerateParameters(params, rand.Reader, sizes)
+ if err != nil {
+ t.Errorf("%d: %s", int(sizes), err)
+ return
+ }
+
+ if params.P.BitLen() != L {
+ t.Errorf("%d: params.BitLen got:%d want:%d", int(sizes), params.P.BitLen(), L)
+ }
+
+ if params.Q.BitLen() != N {
+ t.Errorf("%d: q.BitLen got:%d want:%d", int(sizes), params.Q.BitLen(), L)
+ }
+
+ one := new(big.Int)
+ one.SetInt64(1)
+ pm1 := new(big.Int).Sub(params.P, one)
+ quo, rem := new(big.Int).DivMod(pm1, params.Q, new(big.Int))
+ if rem.Sign() != 0 {
+ t.Errorf("%d: p-1 mod q != 0", int(sizes))
+ }
+ x := new(big.Int).Exp(params.G, quo, params.P)
+ if x.Cmp(one) == 0 {
+ t.Errorf("%d: invalid generator", int(sizes))
+ }
+
+ err = GenerateKey(&priv, rand.Reader)
+ if err != nil {
+ t.Errorf("error generating key: %s", err)
+ return
+ }
+
+ testSignAndVerify(t, int(sizes), &priv)
+}
+
+func TestParameterGeneration(t *testing.T) {
+ // This test is too slow to run all the time.
+ return
+
+ testParameterGeneration(t, L1024N160, 1024, 160)
+ testParameterGeneration(t, L2048N224, 2048, 224)
+ testParameterGeneration(t, L2048N256, 2048, 256)
+ testParameterGeneration(t, L3072N256, 3072, 256)
+}
+
+func TestSignAndVerify(t *testing.T) {
+ var priv PrivateKey
+ priv.P, _ = new(big.Int).SetString("A9B5B793FB4785793D246BAE77E8FF63CA52F442DA763C440259919FE1BC1D6065A9350637A04F75A2F039401D49F08E066C4D275A5A65DA5684BC563C14289D7AB8A67163BFBF79D85972619AD2CFF55AB0EE77A9002B0EF96293BDD0F42685EBB2C66C327079F6C98000FBCB79AACDE1BC6F9D5C7B1A97E3D9D54ED7951FEF", 16)
+ priv.Q, _ = new(big.Int).SetString("E1D3391245933D68A0714ED34BBCB7A1F422B9C1", 16)
+ priv.G, _ = new(big.Int).SetString("634364FC25248933D01D1993ECABD0657CC0CB2CEED7ED2E3E8AECDFCDC4A25C3B15E9E3B163ACA2984B5539181F3EFF1A5E8903D71D5B95DA4F27202B77D2C44B430BB53741A8D59A8F86887525C9F2A6A5980A195EAA7F2FF910064301DEF89D3AA213E1FAC7768D89365318E370AF54A112EFBA9246D9158386BA1B4EEFDA", 16)
+ priv.Y, _ = new(big.Int).SetString("32969E5780CFE1C849A1C276D7AEB4F38A23B591739AA2FE197349AEEBD31366AEE5EB7E6C6DDB7C57D02432B30DB5AA66D9884299FAA72568944E4EEDC92EA3FBC6F39F53412FBCC563208F7C15B737AC8910DBC2D9C9B8C001E72FDC40EB694AB1F06A5A2DBD18D9E36C66F31F566742F11EC0A52E9F7B89355C02FB5D32D2", 16)
+ priv.X, _ = new(big.Int).SetString("5078D4D29795CBE76D3AACFE48C9AF0BCDBEE91A", 16)
+
+ testSignAndVerify(t, 0, &priv)
+}