add sign and verification to ecdsa

This commit adds support to sign and verify messages using ecdsa.

ecdsa.go

@@ -6,8 +6,10 @@ import (
   "crypto/elliptic"
   "crypto/rand"
   "crypto/x509"
+  "encoding/asn1"
   "encoding/pem"
   "errors"
+  "math/big"
 )
 
 const (
@@ -24,6 +26,10 @@ type (
   EcdsaPublicKey struct {
     public_key *ecdsa.PublicKey
   }
+
+  signatureEcdsa struct {
+    R, S *big.Int
+  }
 )
 
 // generate a new ecdsa private key
@@ -46,8 +52,14 @@ func (pr EcdsaPrivateKey) Public() PublicKey {
 }
 
 // sign a message with the private key
-func (pr EcdsaPrivateKey) Sign(message []byte) ([]byte, error) {
-  return make([]byte, 0), errors.New("not implemented yet!")
+func (pr EcdsaPrivateKey) Sign(message []byte, hash crypto.Hash) ([]byte, error) {
+  empty := make([]byte, 0)
+  if !hash.Available() {
+    return empty, errors.New("Hash method is not available!")
+  }
+  hashed_message := hash.New()
+  hashed_message.Write(message)
+  return pr.private_key.Sign(rand.Reader, hashed_message.Sum(nil), hash)
 }
 
 // get the private key
@@ -72,6 +84,11 @@ func (pu *EcdsaPublicKey) MarshalPem() (marshalledPemBlock, error) {
 }
 
 // verify a message using the ecdsa public key
-func (pu *EcdsaPublicKey) Verify(message []byte, signature []byte) (bool, error) {
-  return false, errors.New("not implemented yet!")
+func (pu *EcdsaPublicKey) Verify(message []byte, signature_raw []byte, hash crypto.Hash) (bool, error) {
+  var sig signatureEcdsa
+  _, err := asn1.Unmarshal(signature_raw, &sig)
+  if err != nil { return false, err }
+  hashed_message := hash.New()
+  hashed_message.Write(message)
+  return ecdsa.Verify(pu.public_key, hashed_message.Sum(nil), sig.R, sig.S), nil
 }

private_key_test.go

@@ -1,6 +1,7 @@
 package pki
 
 import (
+  "crypto"
   "crypto/elliptic"
   "encoding/pem"
   "testing"
@@ -8,6 +9,7 @@ import (
 
 var (
   SignatureMessage = []byte("foobar")
+  SignatureHash    = crypto.SHA512
 )
 
 // run the marshal test
@@ -34,10 +36,10 @@ func RunPrivateKeyTests(pk_type string, pk PrivateKey, t *testing.T) {
   _, err := RunMarshalTest(pk_type + "-public", pu, PemLabelPublic, t)
   if err != nil { return }
 
-  signature, err := pk.Sign(SignatureMessage)
+  signature, err := pk.Sign(SignatureMessage, SignatureHash)
   if err != nil { t.Errorf("%s: error creating a signature: %s", pk_type, err) }
 
-  valid, err := pu.Verify(SignatureMessage, signature)
+  valid, err := pu.Verify(SignatureMessage, signature, SignatureHash)
   if err != nil { t.Errorf("%s: could not verify message: %s", pk_type, err) }
   if !valid { t.Errorf("%s: signature invalid, but should be valid!", pk_type) }
 }

rsa.go

@@ -41,7 +41,7 @@ func (pr *RsaPrivateKey) Public() PublicKey {
   return &RsaPublicKey{pr.private_key.Public().(*rsa.PublicKey)}
 }
 
-func (pr RsaPrivateKey) Sign(message []byte) ([]byte, error) {
+func (pr RsaPrivateKey) Sign(message []byte, hash crypto.Hash) ([]byte, error) {
   return make([]byte, 0), errors.New("not implemented yet!")
 }
 
@@ -63,6 +63,6 @@ func (pu *RsaPublicKey) MarshalPem() (marshalledPemBlock, error) {
   return pem.EncodeToMemory(&pem_block), nil
 }
 
-func (pu *RsaPublicKey) Verify(message []byte, signature []byte) (bool, error) {
+func (pu *RsaPublicKey) Verify(message []byte, signature []byte, hash crypto.Hash) (bool, error) {
   return false, errors.New("not implemented yet!")
 }

types.go

@@ -14,8 +14,10 @@ type (
   PrivateKey interface {
     // derive a public key from the private key
     Public() PublicKey
-    // sign a message with the private key
-    Sign(message []byte) ([]byte, error)
+    // Sign a message using the public key and the given hash method.
+    // To use a hash method, include the package
+    //   import _ "crypto/sha512"
+    Sign(message []byte, hash crypto.Hash) ([]byte, error)
 
     // return the private key structure
     privateKey() crypto.PrivateKey
@@ -25,7 +27,7 @@ type (
   PublicKey interface {
     Pemmer
     // use the public key to verify a message against a signature
-    Verify(message []byte, signature []byte) (bool, error)
+    Verify(message []byte, signature []byte, hash crypto.Hash) (bool, error)
   }
 
   Pemmer interface {