I have to encrypt a string in my iPhone app. The encryption scheme is 3DES/CBC/PKCS5 padding and I have to convert in objective-c this Java code:
public class MessageEncrypt {
public String encryptString(String message, String seckey) throws Exception{
byte[] encData = encrypt(message, seckey);
return this.getHexString(encData, "");
}
public String decryptString(String message, String seckey) throws Exception{
return decrypt(this.getBArray(message), seckey);
}
private byte[] encrypt(String message, String seckey) throws Exception {
final MessageDigest md = MessageDigest.getInstance("md5");
final byte[] digestOfPassword = md.digest(seckey.getBytes("utf-8"));
final byte[] keyBytes = acopyof(digestOfPassword, 24);
for (int j = 0, k = 16; j < 8;) {
keyBytes[k++] = keyBytes[j++];
}
final SecretKey key = new SecretKeySpec(keyBytes, "DESede");
final IvParameterSpec iv = new IvParameterSpec(new byte[8]);
final Cipher cipher = Cipher.getInstance("DESede/CBC/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, key, iv);
final byte[] plainTextBytes = message.getBytes("utf-8");
final byte[] cipherText = cipher.doFinal(plainTextBytes);
// final String encodedCipherText = new sun.misc.BASE64Encoder()
// .encode(cipherText);
return cipherText;
}
private String decrypt(byte[] message, String seckey) throws Exception {
final MessageDigest md = MessageDigest.getInstance("md5");
final byte[] digestOfPassword = md.digest(seckey.getBytes("utf-8"));
final byte[] keyBytes = acopyof(digestOfPassword, 24);
for (int j = 0, k = 16; j < 8;) {
keyBytes[k++] = keyBytes[j++];
}
final SecretKey key = new SecretKeySpec(keyBytes, "DESede");
final IvParameterSpec iv = new IvParameterSpec(new byte[8]);
final Cipher decipher = Cipher.getInstance("DESede/CBC/PKCS5Padding");
decipher.init(Cipher.DECRYPT_MODE, key, iv);
final byte[] plainText = decipher.doFinal(message);
return new String(plainText, "UTF-8");
}
private String getHexString(byte[] barray, String delim) {
StringBuffer buffer = new StringBuffer();
for (int i = 0; i < barray.length; i++) {
int ii = barray[i] & 0xFF;
String bInt = Integer.toHexString(ii);
if (ii < 16) {
bInt = "0" + bInt.toUpperCase();
}
buffer.append(bInt);
if (i < barray.length - 1) {
buffer.append(delim);
}
}
return buffer.toString().toUpperCase();
}
private byte[] getBArray(String bString) {
byte[] retBytes;
if (bString.length() % 2 != 0) {
return new byte[0];
}
retBytes = new byte[bString.length() / 2];
for (int i = 0; i < bString.length() / 2; i++) {
retBytes[i] = (byte) ((Character.digit(bString.charAt(2 * i), 16) << 4) + Character.digit(bString.charAt(2 * i + 1), 16));
}
return retBytes;
}
public static byte[] acopyof(byte[] orig, int newlength){
byte[] copya = new byte[newlength];
for(int i=0;i< orig.length;i++){
copya[i]=orig[i];
}
for(int i=orig.length;i<newlength;i++){
copya[i]=0x0;
}
return copya;
}
}
I made this objective-c method to match those specs:
+(NSString*)doCipher:(NSString*)sTextIn:(CCOperation)encryptOrDecrypt {
// const void *vplainText; // size_t plainTextBufferSize;
NSMutableData *dTextIn;
if (encryptOrDecrypt == kCCDecrypt)
{
}
else
{
dTextIn = [[sTextIn dataUsingEncoding: NSASCIIStringEncoding]mutableCopy];
}
NSLog(@"************** Init encrypting **********************************");
NSLog(@"This is data to encrypt %@",dTextIn);
CCCryptorStatus ccStatus;
uint8_t *bufferPtr = NULL;
size_t bufferPtrSize = 0;
size_t movedBytes = 0;
// uint8_t ivkCCBlockSize3DES;
bufferPtrSize = ([dTextIn length] + kCCBlockSize3DES) & ~(kCCBlockSize3DES - 1);
bufferPtr = malloc( bufferPtrSize * sizeof(uint8_t));
memset((void *)bufferPtr, 0x00, bufferPtrSize);
// Initialization vector; in this case 8 bytes.
uint8_t iv[kCCBlockSize3DES];
memset((void *) iv, 0x8, (size_t) sizeof(iv));
UserAndPassword *userPass = [[UserAndPassword alloc]init];
NSString *userPassword = userPass.password;
NSLog(@"This is my password %@",userPassword);
NSString *key = [userPassword MD5String];
NSLog(@"This is MD5 key %@",key);
NSMutableData *_keyData = [[key dataUsingEncoding:NSASCIIStringEncoding]mutableCopy];
unsigned char *bytePtr = (unsigned char *)[_keyData bytes];
NSLog(@"Bytes of key are %s ", bytePtr);
NSLog(@"******** This is my key length %d *******",[_keyData length]);
[_keyData setLength:24];
unsigned char *bytePtr1 = (unsigned char *)[_keyData bytes];
NSLog(@"******** Bytes of key are %s ************", bytePtr1);
NSLog(@"********* This is key length %d ***********",[_keyData length]);
ccStatus = CCCrypt(encryptOrDecrypt, // CCoperation op
kCCAlgorithm3DES, // CCAlgorithm alg
kCCOptionPKCS7Padding, // CCOptions
[_keyData bytes], // const void *key
kCCKeySize3DES, // 3DES key size length 24 bit
iv, //const void *iv,
[dTextIn bytes], // const void *dataIn
[dTextIn length], // size_t dataInLength
(void *)bufferPtr, // void *dataOut
bufferPtrSize, // size_t dataOutAvailable
&movedBytes); // size_t *dataOutMoved
if (ccStatus == kCCParamError) return @"PARAM ERROR";
else if (ccStatus == kCCBufferTooSmall) return @"BUFFER TOO SMALL";
else if (ccStatus == kCCMemoryFailure) return @"MEMORY FAILURE";
else if (ccStatus == kCCAlignmentError) return @"ALIGNMENT";
else if (ccStatus == kCCDecodeError) return @"DECODE ERROR";
else if (ccStatus == kCCUnimplemented) return @"UNIMPLEMENTED";
NSString *result;
if (encryptOrDecrypt == kCCDecrypt)
{
// result = [[NSString alloc] initWithData: [NSData dataWithBytes:(const void *)bufferPtr length:[(NSUInteger)movedBytes] encoding:NSASCIIStringEncoding]];
result = [[[NSString alloc] initWithData:[NSData dataWithBytes:(const void *)bufferPtr length:(NSUInteger)movedBytes] encoding:NSUTF8StringEncoding] autorelease];
}
else
{
NSData *myData = [NSData dataWithBytes:(const void *)bufferPtr length:(NSUInteger)movedBytes];
NSLog(@"This is my encrypted bytes %@", myData);
result = [NSString dataToHex:myData];
NSLog(@"This is my encrypted string %@", result);
NSLog(@"********************** Encryption is finished ************");
}
return result;
}
I didn't manage to match the 3DES encryption obtained with Java code and I don't understand which is the problem.
Thank you in advance, Pier
The Java version is using an IV of 0s, while the Objective-C version uses 8s.
Deriving a key from a password using one round of MD5 and no salt is not secure. Use a key derivation algorithm like PBKDF2.