From 17fa3913ef7ba5f569ebc3695fab15b10dd914f0 Mon Sep 17 00:00:00 2001
From: Jack Grigg <jack@z.cash>
Date: Tue, 6 Jun 2017 19:21:34 +1200
Subject: Specify ECDSA constant sizes as constants

---
 src/key.cpp | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

(limited to 'src/key.cpp')

diff --git a/src/key.cpp b/src/key.cpp
index 31d485722a..3b679414d1 100644
--- a/src/key.cpp
+++ b/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);
-- 
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