crypto: change ECSignatureCreator defaults to match SPDY.

crypto/ec_signature_creator.h

Index: crypto/ec_signature_creator.h
diff --git a/crypto/ec_signature_creator.h b/crypto/ec_signature_creator.h
index b557daaf7b0193d8708fd705e77475572251f823..a3cf88d254a8f666f7bcd5ca6c5e61ee2dbb2c8a 100644
--- a/crypto/ec_signature_creator.h
+++ b/crypto/ec_signature_creator.h
@@ -31,7 +31,7 @@ class CRYPTO_EXPORT ECSignatureCreator {
 
   // Create an instance. The caller must ensure that the provided PrivateKey
   // instance outlives the created ECSignatureCreator.
-  // TODO(rch):  This is currently hard coded to use SHA1. Ideally, we should
+  // TODO(rch):  This is currently hard coded to use SHA256. Ideally, we should
   // pass in the hash algorithm identifier.
   static ECSignatureCreator* Create(ECPrivateKey* key);
 
@@ -42,11 +42,7 @@ class CRYPTO_EXPORT ECSignatureCreator {
   static void SetFactoryForTesting(ECSignatureCreatorFactory* factory);
 
   // Signs |data_len| bytes from |data| and writes the results into
-  // |signature| as a DER encoded ECDSA-Sig-Value from RFC 3279.
-  //
-  //  ECDSA-Sig-Value ::= SEQUENCE {
-  //    r     INTEGER,
-  //    s     INTEGER }
+  // |signature| as a pair of big-endian field elements.

[wtc, 2012/09/12 19:47:45]

The r and s of a signature are integers. (The x,y coordinates
of a point are field elements.)

This comments needs to say the r and s integers are each
big-endian, zero-padded to the right length, and then
concatenated. That right length is hard to describe
concisely (the length in bytes of the order of the curve's
base point). For P-256, that's 32 bytes.

[agl, 2012/09/12 21:41:46]

This is a NIST curve, so x and y are field elements too (of
the scalar field). Although I agree that it might confuse
things to call them that, so I've removed that wording.
Done.

[wtc, 2012/09/12 22:06:27]

For P-256, r and s are integers mod n, whereas x and y are
integers mod p. n and p are both 256-bit primes but are
different. This is why I think it's confusing to say r and
s are field elements, even though they are technically because
n < p.

   virtual bool Sign(const uint8* data,
                     int data_len,
                     std::vector<uint8>* signature) = 0;