Duplicating Java Encryption in Objective C - iphone

Question

This is a continuation of this question, PBEWithMD5AndDES Encryption in iOS, as it was suggested I start a new questions with a different approach.
What I basically need to do here is duplicate some encryption that's happening in an android app, in an iOS app. I have some encryption working, but as it says in the previous question, the encrypted value is inconsistent. I need the encrypted value on the iOS end to be the same as the encrypted value on the android side, because they will be sharing that data. I am including the java function as well as the objective c class. Both sides of this are flexible, I just have limited knowledge of encryption algorithms.
Here's the java function.
public DesEncrypter(String passPhrase) {
try {
// Create the key
KeySpec keySpec = new PBEKeySpec(passPhrase.toCharArray(), salt, iterationCount);
SecretKey key = SecretKeyFactory.getInstance(
"PBEWithMD5AndDES").generateSecret(keySpec);
ecipher = Cipher.getInstance(key.getAlgorithm());
dcipher = Cipher.getInstance(key.getAlgorithm());
// Prepare the parameter to the ciphers
AlgorithmParameterSpec paramSpec = new PBEParameterSpec(salt, iterationCount);
// Create the ciphers
ecipher.init(Cipher.ENCRYPT_MODE, key, paramSpec);
dcipher.init(Cipher.DECRYPT_MODE, key, paramSpec);
} catch (java.security.InvalidAlgorithmParameterException e) {
} catch (java.security.spec.InvalidKeySpecException e) {
} catch (javax.crypto.NoSuchPaddingException e) {
} catch (java.security.NoSuchAlgorithmException e) {
} catch (java.security.InvalidKeyException e) {
}
}
Here's the objective c class.
#implementation CryptoHelper
#pragma mark -
#pragma mark Init Methods
- (id)init
{
if(self = [super init])
{
}
return self;
}
#pragma mark -
#pragma mark String Specific Methods
/**
* Encrypts a string for social blast service.
*
* #param plainString The string to encrypt;
*
* #return NSString The encrypted string.
*/
- (NSString *)encryptString: (NSString *) plainString{
// Convert string to data and encrypt
NSData *data = [self encryptPBEWithMD5AndDESData:[plainString dataUsingEncoding:NSUTF8StringEncoding] password:#"1111"];
// Get encrypted string from data
return [data base64EncodingWithLineLength:1024];
}
/**
* Descrypts a string from social blast service.
*
* #param plainString The string to decrypt;
*
* #return NSString The decrypted string.
*/
- (NSString *)decryptString: (NSString *) encryptedString{
// decrypt the data
NSData * data = [self decryptPBEWithMD5AndDESData:[NSData dataWithBase64EncodedString:encryptedString] password:#"1111"];
// extract and return string
return [NSString stringWithUTF8String:[data bytes]];
}
#pragma mark -
#pragma mark Crypto Methods
- (NSData *)encryptPBEWithMD5AndDESData:(NSData *)inData password:(NSString *)password {
return [self encodePBEWithMD5AndDESData:inData password:password direction:1];
}
- (NSData *)decryptPBEWithMD5AndDESData:(NSData *)inData password:(NSString *)password {
return [self encodePBEWithMD5AndDESData:inData password:password direction:0];
}
- (NSData *)encodePBEWithMD5AndDESData:(NSData *)inData password:(NSString *)password direction:(int)direction
{
NSLog(#"helper data = %#", inData);
static const char gSalt[] =
{
(unsigned char)0xAA, (unsigned char)0xAA, (unsigned char)0xAA, (unsigned char)0xAA,
(unsigned char)0xAA, (unsigned char)0xAA, (unsigned char)0xAA, (unsigned char)0xAA,
(unsigned char)0x00
};
unsigned char *salt = (unsigned char *)gSalt;
int saltLen = strlen(gSalt);
int iterations = 15;
EVP_CIPHER_CTX cipherCtx;
unsigned char *mResults; // allocated storage of results
int mResultsLen = 0;
const char *cPassword = [password UTF8String];
unsigned char *mData = (unsigned char *)[inData bytes];
int mDataLen = [inData length];
SSLeay_add_all_algorithms();
X509_ALGOR *algorithm = PKCS5_pbe_set(NID_pbeWithMD5AndDES_CBC,
iterations, salt, saltLen);
memset(&cipherCtx, 0, sizeof(cipherCtx));
if (algorithm != NULL)
{
EVP_CIPHER_CTX_init(&(cipherCtx));
if (EVP_PBE_CipherInit(algorithm->algorithm, cPassword, strlen(cPassword),
algorithm->parameter, &(cipherCtx), direction))
{
EVP_CIPHER_CTX_set_padding(&cipherCtx, 1);
int blockSize = EVP_CIPHER_CTX_block_size(&cipherCtx);
int allocLen = mDataLen + blockSize + 1; // plus 1 for null terminator on decrypt
mResults = (unsigned char *)OPENSSL_malloc(allocLen);
unsigned char *in_bytes = mData;
int inLen = mDataLen;
unsigned char *out_bytes = mResults;
int outLen = 0;
int outLenPart1 = 0;
if (EVP_CipherUpdate(&(cipherCtx), out_bytes, &outLenPart1, in_bytes, inLen))
{
out_bytes += outLenPart1;
int outLenPart2 = 0;
if (EVP_CipherFinal(&(cipherCtx), out_bytes, &outLenPart2))
{
outLen += outLenPart1 + outLenPart2;
mResults[outLen] = 0;
mResultsLen = outLen;
}
} else {
unsigned long err = ERR_get_error();
ERR_load_crypto_strings();
ERR_load_ERR_strings();
char errbuff[256];
errbuff[0] = 0;
ERR_error_string_n(err, errbuff, sizeof(errbuff));
NSLog(#"OpenSLL ERROR:\n\tlib:%s\n\tfunction:%s\n\treason:%s\n",
ERR_lib_error_string(err),
ERR_func_error_string(err),
ERR_reason_error_string(err));
ERR_free_strings();
}
NSData *encryptedData = [NSData dataWithBytes:mResults length:mResultsLen]; //(NSData *)encr_buf;
//NSLog(#"encryption result: %#\n", [encryptedData base64EncodingWithLineLength:1024]);
EVP_cleanup();
return encryptedData;
}
}
EVP_cleanup();
return nil;
}
#end
I'm using an openssl static library for ios.
Thanks,
Brandon

Answer 1

For encryption to work correctly everything needs to be exactly the same at both ends. The same mode, the same key, the same IV and the same padding. You need to check each of these. Don't rely on the default mode but explicitly specify CBC (or CTR) at both ends. After generating your key, print it in hex on both ends so you can check that it is identical. Print the IV in hex at both ends to check. Don't rely on the defaults but explicitly specify the padding (PKCS5 or PKCS7) on both ends.
I have also seen problems with cyphertext where is is converted into a string in one character encoding but converted back to bytes as if it was in another character encoding. Make sure that you are using the same character encoding at both ends.
Once you have identified where the mismatches are happening you can fix them.
On a side note I notice that you are using DES. This is now obsolete and should only be used for backwards compatibility. Use AES for all new applications.