implement `crypto.cc` with OpenSSL + fix config loading

  I considered reversing the original `vlong` implementation but
OpenSSL is just simpler, more secure, and most importantly, is
already there. I also made it so the key is now stored in a PEM
file (`tibia.pem`) so it can be easily swapped without re-compiling.

  This was the last piece to build and run a working executable,
except that we now need to implement a query manager for the server
to communicate with. I was able to fix a small problem with loading
the config before hitting the problem with the query manager, which
was expected.

  The next task should be getting a query manager up and running
before starting phase two of upgrading and fixing the server itself.

1 files changed, 106 insertions, 1 deletions

diff --git a/src/crypto.cc b/src/crypto.cc
index b6df866..aa53dc3 100644
--- a/src/crypto.cc
+++ b/src/crypto.cc
@@ -1,3 +1,108 @@
 #include "crypto.hh"
 
-// TODO
+#include <openssl/err.h>
+#include <openssl/pem.h>
+
+static void DumpOpenSSLErrors(const char *Where, const char *What){
+	error("OpenSSL error(s) while executing %s at %s:\n", What, Where);
+	ERR_print_errors_cb(
+		[](const char *str, usize len, void *u) -> int {
+			// NOTE(fusion): These error strings already have trailing newlines,
+			// for whatever reason.
+			error("> %s", str);
+			return 1;
+		}, NULL);
+}
+
+// TRSAPrivateKey
+// =============================================================================
+TRSAPrivateKey::TRSAPrivateKey(void){
+	m_RSA = NULL;
+}
+
+TRSAPrivateKey::~TRSAPrivateKey(void){
+	if(m_RSA){
+		RSA_free(m_RSA);
+		m_RSA = NULL;
+	}
+}
+
+void TRSAPrivateKey::initFromFile(const char *FileName){
+	if(m_RSA != NULL){
+		error("TRSAPrivateKey::init: Key already initialized.\n");
+		return;
+	}
+
+	FILE *File = fopen(FileName, "rb");
+	if(File == NULL){
+		error("TRSAPrivateKey::initFromFile: Failed to open \"%s\".\n", FileName);
+		return;
+	}
+
+	m_RSA = PEM_read_RSAPrivateKey(File, NULL, NULL, NULL);
+	fclose(File);
+
+	if(m_RSA == NULL){
+		error("TRSAPrivateKey::initFromFile: Failed to read key from \"%s\".\n", FileName);
+		DumpOpenSSLErrors("TRSAPrivateKey::initFromFile", "PEM_read_RSAPrivateKey");
+	}else if(RSA_size(m_RSA) != 128){
+		error("TRSAPrivateKey::initFromFile: File \"%s\" doesn't contain a 1024-bit key", FileName);
+		RSA_free(m_RSA);
+		m_RSA = NULL;
+	}
+}
+
+void TRSAPrivateKey::decrypt(uint8 *Data){
+	if(m_RSA == NULL){
+		error("TRSAPrivateKey::decrypt: Key not initialized.\n");
+		return;
+	}
+
+	// TODO(fusion): Pass in the length of `Data` for checking.
+	ASSERT(RSA_size(m_RSA) == 128);
+
+	if(RSA_private_decrypt(128, Data, Data, m_RSA, RSA_NO_PADDING) == -1){
+		DumpOpenSSLErrors("TRSAPrivateKey::decrypt", "RSA_private_decrypt");
+	}
+}
+
+// TXTEASymmetricKey
+// =============================================================================
+void TXTEASymmetricKey::init(TReadBuffer *Buffer){
+	m_SymmetricKey[0] = Buffer->readQuad();
+	m_SymmetricKey[1] = Buffer->readQuad();
+	m_SymmetricKey[2] = Buffer->readQuad();
+	m_SymmetricKey[3] = Buffer->readQuad();
+}
+
+void TXTEASymmetricKey::encrypt(uint8 *Data){
+	// TODO(fusion): This assumes both data endpoints have the same byte order.
+	// It's unlikely that there is anything other than little-endian but we
+	// should use a few helping functions to ensure compatibility.
+	uint32 Sum = 0x00000000UL;
+	uint32 Delta = 0x9E3779B9UL;
+	uint32 V0 = *(uint32*)(&Data[0]);
+	uint32 V1 = *(uint32*)(&Data[4]);
+	for(int i = 0; i < 32; i += 1){
+		V0 += (((V1 << 4) ^ (V1 >> 5)) + V1) ^ (Sum + m_SymmetricKey[Sum & 3]);
+		Sum += Delta;
+		V1 += (((V0 << 4) ^ (V0 >> 5)) + V0) ^ (Sum + m_SymmetricKey[(Sum >> 11) & 3]);
+	}
+	*(uint32*)(&Data[0]) = V0;
+	*(uint32*)(&Data[4]) = V1;
+}
+
+void TXTEASymmetricKey::decrypt(uint8 *Data){
+	// TODO(fusion): Same as above.
+	uint32 Sum = 0xC6EF3720UL;
+	uint32 Delta = 0x9E3779B9UL;
+	uint32 V0 = *(uint32*)(&Data[0]);
+	uint32 V1 = *(uint32*)(&Data[4]);
+	for(int i = 0; i < 32; i += 1){
+		V1 -= (((V0 << 4) ^ (V0 >> 5)) + V0) ^ (Sum + m_SymmetricKey[(Sum >> 11) & 3]);
+		Sum -= Delta;
+		V0 -= (((V1 << 4) ^ (V1 >> 5)) + V1) ^ (Sum + m_SymmetricKey[Sum & 3]);
+	}
+	*(uint32*)(&Data[0]) = V0;
+	*(uint32*)(&Data[4]) = V1;
+}