1 files changed, 34 insertions, 0 deletions

diff --git a/lib/cryptopp/emsa2.cpp b/lib/cryptopp/emsa2.cpp
new file mode 100644
index 000000000..3dbb7e8c0
--- /dev/null
+++ b/lib/cryptopp/emsa2.cpp
@@ -0,0 +1,34 @@
+// emsa2.cpp - written and placed in the public domain by Wei Dai
+
+#include "pch.h"
+#include "emsa2.h"
+
+#ifndef CRYPTOPP_IMPORTS
+
+NAMESPACE_BEGIN(CryptoPP)
+
+void EMSA2Pad::ComputeMessageRepresentative(RandomNumberGenerator &rng, 
+	const byte *recoverableMessage, size_t recoverableMessageLength,
+	HashTransformation &hash, HashIdentifier hashIdentifier, bool messageEmpty,
+	byte *representative, size_t representativeBitLength) const
+{
+	assert(representativeBitLength >= MinRepresentativeBitLength(hashIdentifier.second, hash.DigestSize()));
+
+	if (representativeBitLength % 8 != 7)
+		throw PK_SignatureScheme::InvalidKeyLength("EMSA2: EMSA2 requires a key length that is a multiple of 8");
+
+	size_t digestSize = hash.DigestSize();
+	size_t representativeByteLength = BitsToBytes(representativeBitLength);
+
+	representative[0] = messageEmpty ? 0x4b : 0x6b;
+	memset(representative+1, 0xbb, representativeByteLength-digestSize-4);	// pad with 0xbb
+	byte *afterP2 = representative+representativeByteLength-digestSize-3;
+	afterP2[0] = 0xba;
+	hash.Final(afterP2+1);
+	representative[representativeByteLength-2] = *hashIdentifier.first;
+	representative[representativeByteLength-1] = 0xcc;
+}
+
+NAMESPACE_END
+
+#endif