Exemple #1
0
/* Encrypts a string "message" using "key". */
std::string RSA::encryptString(const std::string &message, const Key &key)
{
	//partition the message into biggest possible encryptable chunks
	const unsigned long int chunkSize(((key.GetModulus().Length() - 2) / 3));
	const unsigned long int chunkCount = message.length() / chunkSize;

	string cypherText;
	for (unsigned long int i(0); i < chunkCount; i++)
	{
		// Get the next chunk.
		string chunk(message.substr(i * chunkSize, chunkSize));
		chunk = RSA::encryptChunk(chunk, key);
		// Put a ' ' between the chunks so that we can separate them later. 
		cypherText.append(chunk.append(" "));
	}
	// If the last chunk has the same size as the others, we are finished. 
	if (chunkSize * chunkCount == message.length())
		return cypherText;

	// Handle the last chunk. It is smaller than the others. 
	const unsigned long int lastChunkSize = message.length() % chunkSize;
	string lastChunk(message.substr(chunkCount * chunkSize, lastChunkSize));
	lastChunk = RSA::encryptChunk(lastChunk, key);
	return cypherText.append(lastChunk.append(" "));
}
Exemple #2
0
/* Decrypts a "chunk" (a small part of a message) using "key" */
string RSA::decryptChunk(const BigInt &chunk, const Key &key)
{
	BigInt a = chunk;
	// The RSA decryption algorithm is a congruence equation. 
	a.SetPowerMod(key.GetExponent(), key.GetModulus());
	// Decode the message to a readable form. 
	return RSA::decode(a);
}
Exemple #3
0
/* Encrypts a "chunk" (a small part of a message) using "key" */
string RSA::encryptChunk(const string &chunk, const Key &key)
{
	// First encode the chunk, to make sure it is represented as an integer. 
	BigInt a = RSA::encode(chunk);
	// The RSA encryption algorithm is a congruence equation. 
	a.SetPowerMod(key.GetExponent(), key.GetModulus());
	return a.ToString();
}
Exemple #4
0
/* Decrypts a string "message" using "key". */
std::string RSA::decryptString(const std::string &cypherText, const Key &key)
{
	// Partition the cypherText into chunks. They are seperated by ' '. 
	string message;
	long int i(0), j(0);
	while ((j = cypherText.find(' ', i)) != -1)
	{
		// Get the chunk. 
		BigInt chunk(cypherText.substr(i, j - i));
		if (chunk >= key.GetModulus())
			throw "Error RSA02: Chunk too large.";

		// Decrypt the chunk and store the message. 
		string text = RSA::decryptChunk(chunk, key);
		message.append(text);
		i = j + 1;
	}
	return message;
}
Exemple #5
0
/* Throws an exception if "key" is too short to be used. */
void RSA::checkKeyLength(const Key &key)
{
	// Minimum required key length is around 24 bits. (In-house requirement)
	if (key.GetModulus().Length() < 8)
		throw "Error RSA01: Keys must be at least 8 digits long.";
}