diff --git a/hmac.h b/hmac.h
new file mode 100644
index 00000000..7b77af28
--- /dev/null
+++ b/hmac.h
@@ -0,0 +1,60 @@
+#ifndef HMAC_H__
+#define HMAC_H__
+
+#include <inttypes.h>
+#include <string.h>
+#define CRYPTOPP_ENABLE_NAMESPACE_WEAK 1
+#include <cryptopp/md5.h>
+
+namespace i2p
+{
+namespace crypto
+{
+	const uint64_t IPAD = 0x3636363636363636;
+	const uint64_t OPAD = 0x5C5C5C5C5C5C5C5C; 			
+
+	inline void HMACMD5Digest (uint8_t * msg, size_t len, uint8_t * key, uint8_t * digest)
+	// key is 32 bytes
+	// digest is 16 bytes
+	// block size is 64 bytes	
+	{
+		size_t totalLen = len + 64 + 32; 
+		uint8_t * buf = new uint8_t[totalLen]; // TODO: reuse buffers
+		// ikeypad
+		((uint64_t *)buf)[0] = ((uint64_t *)key)[0] ^ IPAD; 
+		((uint64_t *)buf)[1] = ((uint64_t *)key)[1] ^ IPAD; 
+		((uint64_t *)buf)[2] = ((uint64_t *)key)[2] ^ IPAD; 
+		((uint64_t *)buf)[3] = ((uint64_t *)key)[3] ^ IPAD; 
+		((uint64_t *)buf)[4] = IPAD; 
+		((uint64_t *)buf)[5] = IPAD; 
+		((uint64_t *)buf)[6] = IPAD; 
+		((uint64_t *)buf)[7] = IPAD; 		
+		// concatenate with msg
+		memcpy (buf + 64, msg, len);
+		// calculate first hash
+		uint8_t hash[16]; // MD5
+		CryptoPP::Weak1::MD5().CalculateDigest (hash, buf, len + 64);
+		
+		// okeypad			
+		((uint64_t *)buf)[0] = ((uint64_t *)key)[0] ^ OPAD; 
+		((uint64_t *)buf)[1] = ((uint64_t *)key)[1] ^ OPAD; 
+		((uint64_t *)buf)[2] = ((uint64_t *)key)[2] ^ OPAD; 
+		((uint64_t *)buf)[3] = ((uint64_t *)key)[3] ^ OPAD; 
+		((uint64_t *)buf)[4] = OPAD; 
+		((uint64_t *)buf)[5] = OPAD; 
+		((uint64_t *)buf)[6] = OPAD; 
+		((uint64_t *)buf)[7] = OPAD; 
+		// copy first hash after okeypad		
+		memcpy (buf + 64, hash, 16);
+		// fill next 16 bytes with zeros (first hash size assumed 32 bytes in I2P)
+		memset (buf + 72, 0, 16);			
+		
+		// calculate digest
+		CryptoPP::Weak1::MD5().CalculateDigest (digest, buf, totalLen);
+		delete[] buf;
+	}
+}
+}
+
+#endif
+