Specify ECDSA constant sizes as constants

src/key.cpp

@@ -87,9 +87,13 @@ static int ec_privkey_import_der(const secp256k1_context* ctx, unsigned char *ou
  * <http://www.secg.org/sec1-v2.pdf>. The optional parameters and publicKey fields are
  * included.
  *
+ * privkey must point to an output buffer of length at least PRIVATE_KEY_SIZE bytes.
+ * privkeylen must initially be set to the size of the privkey buffer. Upon return it
+ * will be set to the number of bytes used in the buffer.
  * key32 must point to a 32-byte raw private key.
  */
 static int ec_privkey_export_der(const secp256k1_context *ctx, unsigned char *privkey, size_t *privkeylen, const unsigned char *key32, int compressed) {
+    assert(*privkeylen >= PRIVATE_KEY_SIZE);
     secp256k1_pubkey pubkey;
     size_t pubkeylen = 0;
     if (!secp256k1_ec_pubkey_create(ctx, &pubkey, key32)) {
@@ -115,10 +119,11 @@ static int ec_privkey_export_der(const secp256k1_context *ctx, unsigned char *pr
         memcpy(ptr, begin, sizeof(begin)); ptr += sizeof(begin);
         memcpy(ptr, key32, 32); ptr += 32;
         memcpy(ptr, middle, sizeof(middle)); ptr += sizeof(middle);
-        pubkeylen = 33;
+        pubkeylen = COMPRESSED_PUBLIC_KEY_SIZE;
         secp256k1_ec_pubkey_serialize(ctx, ptr, &pubkeylen, &pubkey, SECP256K1_EC_COMPRESSED);
         ptr += pubkeylen;
         *privkeylen = ptr - privkey;
+        assert(*privkeylen == COMPRESSED_PRIVATE_KEY_SIZE);
     } else {
         static const unsigned char begin[] = {
             0x30,0x82,0x01,0x13,0x02,0x01,0x01,0x04,0x20
@@ -140,10 +145,11 @@ static int ec_privkey_export_der(const secp256k1_context *ctx, unsigned char *pr
         memcpy(ptr, begin, sizeof(begin)); ptr += sizeof(begin);
         memcpy(ptr, key32, 32); ptr += 32;
         memcpy(ptr, middle, sizeof(middle)); ptr += sizeof(middle);
-        pubkeylen = 65;
+        pubkeylen = PUBLIC_KEY_SIZE;
         secp256k1_ec_pubkey_serialize(ctx, ptr, &pubkeylen, &pubkey, SECP256K1_EC_UNCOMPRESSED);
         ptr += pubkeylen;
         *privkeylen = ptr - privkey;
+        assert(*privkeylen == PRIVATE_KEY_SIZE);
     }
     return 1;
 }
@@ -165,8 +171,8 @@ CPrivKey CKey::GetPrivKey() const {
     CPrivKey privkey;
     int ret;
     size_t privkeylen;
-    privkey.resize(279);
-    privkeylen = 279;
+    privkey.resize(PRIVATE_KEY_SIZE);
+    privkeylen = PRIVATE_KEY_SIZE;
     ret = ec_privkey_export_der(secp256k1_context_sign, (unsigned char*) privkey.data(), &privkeylen, begin(), fCompressed ? SECP256K1_EC_COMPRESSED : SECP256K1_EC_UNCOMPRESSED);
     assert(ret);
     privkey.resize(privkeylen);
@@ -176,7 +182,7 @@ CPrivKey CKey::GetPrivKey() const {
 CPubKey CKey::GetPubKey() const {
     assert(fValid);
     secp256k1_pubkey pubkey;
-    size_t clen = 65;
+    size_t clen = PUBLIC_KEY_SIZE;
     CPubKey result;
     int ret = secp256k1_ec_pubkey_create(secp256k1_context_sign, &pubkey, begin());
     assert(ret);
@@ -189,8 +195,8 @@ CPubKey CKey::GetPubKey() const {
 bool CKey::Sign(const uint256 &hash, std::vector<unsigned char>& vchSig, uint32_t test_case) const {
     if (!fValid)
         return false;
-    vchSig.resize(72);
-    size_t nSigLen = 72;
+    vchSig.resize(SIGNATURE_SIZE);
+    size_t nSigLen = SIGNATURE_SIZE;
     unsigned char extra_entropy[32] = {0};
     WriteLE32(extra_entropy, test_case);
     secp256k1_ecdsa_signature sig;
@@ -218,7 +224,7 @@ bool CKey::VerifyPubKey(const CPubKey& pubkey) const {
 bool CKey::SignCompact(const uint256 &hash, std::vector<unsigned char>& vchSig) const {
     if (!fValid)
         return false;
-    vchSig.resize(65);
+    vchSig.resize(COMPACT_SIGNATURE_SIZE);
     int rec = -1;
     secp256k1_ecdsa_recoverable_signature sig;
     int ret = secp256k1_ecdsa_sign_recoverable(secp256k1_context_sign, &sig, hash.begin(), begin(), secp256k1_nonce_function_rfc6979, NULL);
@@ -248,7 +254,7 @@ bool CKey::Derive(CKey& keyChild, ChainCode &ccChild, unsigned int nChild, const
     std::vector<unsigned char, secure_allocator<unsigned char>> vout(64);
     if ((nChild >> 31) == 0) {
         CPubKey pubkey = GetPubKey();
-        assert(pubkey.size() == 33);
+        assert(pubkey.size() == COMPRESSED_PUBLIC_KEY_SIZE);
         BIP32Hash(cc, nChild, *pubkey.begin(), pubkey.begin()+1, vout.data());
     } else {
         assert(size() == 32);

src/key.h

@@ -1,5 +1,6 @@
 // Copyright (c) 2009-2010 Satoshi Nakamoto
 // Copyright (c) 2009-2016 The Bitcoin Core developers
+// Copyright (c) 2017 The Zcash developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -17,17 +18,18 @@
 
 /**
  * secp256k1:
- * const unsigned int PRIVATE_KEY_SIZE = 279;
- * const unsigned int PUBLIC_KEY_SIZE  = 65;
- * const unsigned int SIGNATURE_SIZE   = 72;
- *
+ */
+const unsigned int PRIVATE_KEY_SIZE            = 279;
+const unsigned int COMPRESSED_PRIVATE_KEY_SIZE = 214;
+/**
  * see www.keylength.com
  * script supports up to 75 for single byte push
  */
 
 /**
  * secure_allocator is defined in allocators.h
- * CPrivKey is a serialized private key, with all parameters included (279 bytes)
+ * CPrivKey is a serialized private key, with all parameters included
+ * (PRIVATE_KEY_SIZE bytes)
  */
 typedef std::vector<unsigned char, secure_allocator<unsigned char> > CPrivKey;
 

src/pubkey.cpp

@@ -185,7 +185,7 @@ bool CPubKey::Verify(const uint256 &hash, const std::vector<unsigned char>& vchS
 }
 
 bool CPubKey::RecoverCompact(const uint256 &hash, const std::vector<unsigned char>& vchSig) {
-    if (vchSig.size() != 65)
+    if (vchSig.size() != COMPACT_SIGNATURE_SIZE)
         return false;
     int recid = (vchSig[0] - 27) & 3;
     bool fComp = ((vchSig[0] - 27) & 4) != 0;
@@ -197,8 +197,8 @@ bool CPubKey::RecoverCompact(const uint256 &hash, const std::vector<unsigned cha
     if (!secp256k1_ecdsa_recover(secp256k1_context_verify, &pubkey, &sig, hash.begin())) {
         return false;
     }
-    unsigned char pub[65];
-    size_t publen = 65;
+    unsigned char pub[PUBLIC_KEY_SIZE];
+    size_t publen = PUBLIC_KEY_SIZE;
     secp256k1_ec_pubkey_serialize(secp256k1_context_verify, pub, &publen, &pubkey, fComp ? SECP256K1_EC_COMPRESSED : SECP256K1_EC_UNCOMPRESSED);
     Set(pub, pub + publen);
     return true;
@@ -218,8 +218,8 @@ bool CPubKey::Decompress() {
     if (!secp256k1_ec_pubkey_parse(secp256k1_context_verify, &pubkey, &(*this)[0], size())) {
         return false;
     }
-    unsigned char pub[65];
-    size_t publen = 65;
+    unsigned char pub[PUBLIC_KEY_SIZE];
+    size_t publen = PUBLIC_KEY_SIZE;
     secp256k1_ec_pubkey_serialize(secp256k1_context_verify, pub, &publen, &pubkey, SECP256K1_EC_UNCOMPRESSED);
     Set(pub, pub + publen);
     return true;
@@ -228,7 +228,7 @@ bool CPubKey::Decompress() {
 bool CPubKey::Derive(CPubKey& pubkeyChild, ChainCode &ccChild, unsigned int nChild, const ChainCode& cc) const {
     assert(IsValid());
     assert((nChild >> 31) == 0);
-    assert(size() == 33);
+    assert(size() == COMPRESSED_PUBLIC_KEY_SIZE);
     unsigned char out[64];
     BIP32Hash(cc, nChild, *begin(), begin()+1, out);
     memcpy(ccChild.begin(), out+32, 32);
@@ -239,8 +239,8 @@ bool CPubKey::Derive(CPubKey& pubkeyChild, ChainCode &ccChild, unsigned int nChi
     if (!secp256k1_ec_pubkey_tweak_add(secp256k1_context_verify, &pubkey, out)) {
         return false;
     }
-    unsigned char pub[33];
-    size_t publen = 33;
+    unsigned char pub[COMPRESSED_PUBLIC_KEY_SIZE];
+    size_t publen = COMPRESSED_PUBLIC_KEY_SIZE;
     secp256k1_ec_pubkey_serialize(secp256k1_context_verify, pub, &publen, &pubkey, SECP256K1_EC_COMPRESSED);
     pubkeyChild.Set(pub, pub + publen);
     return true;
@@ -252,8 +252,8 @@ void CExtPubKey::Encode(unsigned char code[BIP32_EXTKEY_SIZE]) const {
     code[5] = (nChild >> 24) & 0xFF; code[6] = (nChild >> 16) & 0xFF;
     code[7] = (nChild >>  8) & 0xFF; code[8] = (nChild >>  0) & 0xFF;
     memcpy(code+9, chaincode.begin(), 32);
-    assert(pubkey.size() == 33);
-    memcpy(code+41, pubkey.begin(), 33);
+    assert(pubkey.size() == COMPRESSED_PUBLIC_KEY_SIZE);
+    memcpy(code+41, pubkey.begin(), COMPRESSED_PUBLIC_KEY_SIZE);
 }
 
 void CExtPubKey::Decode(const unsigned char code[BIP32_EXTKEY_SIZE]) {

src/pubkey.h

@@ -1,5 +1,6 @@
 // Copyright (c) 2009-2010 Satoshi Nakamoto
 // Copyright (c) 2009-2016 The Bitcoin Core developers
+// Copyright (c) 2017 The Zcash developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -15,10 +16,12 @@
 
 /**
  * secp256k1:
- * const unsigned int PRIVATE_KEY_SIZE = 279;
- * const unsigned int PUBLIC_KEY_SIZE  = 65;
- * const unsigned int SIGNATURE_SIZE   = 72;
- *
+ */
+const unsigned int PUBLIC_KEY_SIZE             = 65;
+const unsigned int COMPRESSED_PUBLIC_KEY_SIZE  = 33;
+const unsigned int SIGNATURE_SIZE              = 72;
+const unsigned int COMPACT_SIGNATURE_SIZE      = 65;
+/**
  * see www.keylength.com
  * script supports up to 75 for single byte push
  */
@@ -44,15 +47,15 @@ private:
      * Just store the serialized data.
      * Its length can very cheaply be computed from the first byte.
      */
-    unsigned char vch[65];
+    unsigned char vch[PUBLIC_KEY_SIZE];
 
     //! Compute the length of a pubkey with a given first byte.
     unsigned int static GetLen(unsigned char chHeader)
     {
         if (chHeader == 2 || chHeader == 3)
-            return 33;
+            return COMPRESSED_PUBLIC_KEY_SIZE;
         if (chHeader == 4 || chHeader == 6 || chHeader == 7)
-            return 65;
+            return PUBLIC_KEY_SIZE;
         return 0;
     }
 
@@ -127,7 +130,7 @@ public:
     void Unserialize(Stream& s)
     {
         unsigned int len = ::ReadCompactSize(s);
-        if (len <= 65) {
+        if (len <= PUBLIC_KEY_SIZE) {
             s.read((char*)vch, len);
         } else {
             // invalid pubkey, skip available data
@@ -166,7 +169,7 @@ public:
     //! Check whether this is a compressed public key.
     bool IsCompressed() const
     {
-        return size() == 33;
+        return size() == COMPRESSED_PUBLIC_KEY_SIZE;
     }
 
     /**