fixed bug with chacha20 encryption of short messages

libi2pd/ChaCha20.cpp

@@ -111,7 +111,8 @@ void Chacha20Encrypt (Chacha20State& state, uint8_t * buf, size_t sz)
 			buf[i] ^= state.block.data[state.offset + i];
 		buf += s;
 		sz -= s;
-		state.offset = 0;
+		state.offset += s;
+		if (state.offset >= chacha::blocksize) state.offset = 0;	
 	}
 	for (size_t i = 0; i < sz; i += chacha::blocksize) 
 	{

tests/test-aeadchacha20poly1305.cpp

@@ -53,7 +53,7 @@ int main ()
 	assert (memcmp (buf1, text, 114) == 0);
 	// test encryption of multiple buffers
 	memcpy (buf, text, 114);
-	std::vector<std::pair<uint8_t*, std::size_t> > bufs{ std::make_pair (buf, 50), std::make_pair (buf + 50, 50), std::make_pair (buf + 100, 14) };  
+	std::vector<std::pair<uint8_t*, std::size_t> > bufs{ std::make_pair (buf, 20), std::make_pair (buf + 20, 10), std::make_pair (buf + 30, 70), std::make_pair (buf + 100, 14) };  
 	i2p::crypto::AEADChaCha20Poly1305Encrypt (bufs, key, nonce, buf + 114);
 	i2p::crypto::AEADChaCha20Poly1305 (buf, 114, nullptr, 0, key, nonce, buf1, 114, false);
 	assert (memcmp (buf1, text, 114) == 0);