consensus: guard against openssl's new strict DER checks

New versions of OpenSSL will reject non-canonical DER signatures. However,
it'll happily decode them. Decode then re-encode before verification in order
to ensure that it is properly consumed.

Github-Pull: #5634
Rebased-From: 488ed32f2ada1d1dd108fc245d025c4d5f252783

1 files changed, 13 insertions, 3 deletions

diff --git a/src/ecwrapper.cpp b/src/ecwrapper.cpp
index 5ce7e61294..be33913d0d 100644
--- a/src/ecwrapper.cpp
+++ b/src/ecwrapper.cpp
@@ -117,10 +117,20 @@ bool CECKey::SetPubKey(const unsigned char* pubkey, size_t size) {
 }
 
 bool CECKey::Verify(const uint256 &hash, const std::vector<unsigned char>& vchSig) {
-    // -1 = error, 0 = bad sig, 1 = good
-    if (ECDSA_verify(0, (unsigned char*)&hash, sizeof(hash), &vchSig[0], vchSig.size(), pkey) != 1)
+    // New versions of OpenSSL will reject non-canonical DER signatures. de/re-serialize first.
+    unsigned char *norm_der = NULL;
+    ECDSA_SIG *norm_sig = ECDSA_SIG_new();
+    const unsigned char* sigptr = &vchSig[0];
+    d2i_ECDSA_SIG(&norm_sig, &sigptr, vchSig.size());
+    int derlen = i2d_ECDSA_SIG(norm_sig, &norm_der);
+    ECDSA_SIG_free(norm_sig);
+    if (derlen <= 0)
         return false;
-    return true;
+
+    // -1 = error, 0 = bad sig, 1 = good
+    bool ret = ECDSA_verify(0, (unsigned char*)&hash, sizeof(hash), norm_der, derlen, pkey) == 1;
+    OPENSSL_free(norm_der);
+    return ret;
 }
 
 bool CECKey::Recover(const uint256 &hash, const unsigned char *p64, int rec)