From ac7a367950089af978a398f57010315ff355097e Mon Sep 17 00:00:00 2001
From: Geert-Johan Riemer <geertjohan.riemer@gmail.com>
Date: Thu, 15 May 2014 10:48:52 +0200
Subject: [PATCH] Add type PrivateKey, (*PrivateKey).Sign() and
 (*PublicKey).Verify().

---
 privkey.go | 28 ++++++++++++++++++++++++++--
 pubkey.go  |  6 ++++++
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/privkey.go b/privkey.go
index 8631f222..ad1dfc1f 100644
--- a/privkey.go
+++ b/privkey.go
@@ -6,12 +6,17 @@ package btcec
 
 import (
 	"crypto/ecdsa"
+	"crypto/rand"
 	"math/big"
 )
 
+// PrivateKey is an ecdsa.PrivateKey
+// It provides a method Sign
+type PrivateKey ecdsa.PrivateKey
+
 // PrivKeyFromBytes returns a private and public key for `curve' based on the
 // private key passed as an argument as a byte slice.
-func PrivKeyFromBytes(curve *KoblitzCurve, pk []byte) (*ecdsa.PrivateKey,
+func PrivKeyFromBytes(curve *KoblitzCurve, pk []byte) (*PrivateKey,
 	*PublicKey) {
 	x, y := curve.ScalarBaseMult(pk)
 
@@ -24,5 +29,24 @@ func PrivKeyFromBytes(curve *KoblitzCurve, pk []byte) (*ecdsa.PrivateKey,
 		D: new(big.Int).SetBytes(pk),
 	}
 
-	return priv, (*PublicKey)(&priv.PublicKey)
+	return (*PrivateKey)(priv), (*PublicKey)(&priv.PublicKey)
+}
+
+// ToECDSA returns the private key as a *ecdsa.PrivateKey.
+func (p *PrivateKey) ToECDSA() *ecdsa.PrivateKey {
+	return (*ecdsa.PrivateKey)(p)
+}
+
+// Sign wraps ecdsa.Sign to sign an arbitrary length hash (which should be the result of hashing a larger message) using the private key.
+// It returns the signature as a *Signature. The security of the private key depends on the entropy of rand (crypto/rand.Reader).
+func (p *PrivateKey) Sign(hash []byte) (*Signature, error) {
+	r, s, err := ecdsa.Sign(rand.Reader, p.ToECDSA(), hash)
+	if err != nil {
+		return nil, err
+	}
+	sig := &Signature{
+		R: r,
+		S: s,
+	}
+	return sig, nil
 }
diff --git a/pubkey.go b/pubkey.go
index cf0da666..0d7d679d 100644
--- a/pubkey.go
+++ b/pubkey.go
@@ -162,3 +162,9 @@ func paddedAppend(size uint, dst, src []byte) []byte {
 	}
 	return append(dst, src...)
 }
+
+// Verify calls ecdsa.Verify to verify the signature of hash using the public key.
+// Its return value records whether the signature is valid.
+func (p *PublicKey) Verify(hash []byte, sig *Signature) bool {
+	return ecdsa.Verify(p.ToECDSA(), hash, sig.R, sig.S)
+}