This has stumped me - the following code uses SpongyCastle's encryption/decryption for Android - I am trying to achieve cross-platform encryption/decryption for iOS.
The following code (from Android) works a treat, AES 128bit CBC with PKCS7Padding, using a supplied salt and password, which the salt is stored on the mysql database, the password is by the end-user, the following code is adapted from this answer by kelhoer.
The reason I used AES128bit is that AES256 is not available in iOS 4+, it was introduced in iOS5+, and having to dip the toe into using openssl
to generate a derived key and initialization vector (iv), it was dicey as learnt that Apple rejects apps that are statically linked with openssl library.
Since the platform is based on iOS 4.2+, having resorted to bundling and statically linking the openssl library seems rather, over-kill and would preferably use the CommonCryptor library.
Here's the Android version with Spongycastle code in place:
private static void encrypt(InputStream fin,
OutputStream fout,
String password,
byte[] bSalt) {
try {
PKCS12ParametersGenerator pGen = new PKCS12ParametersGenerator(
new SHA256Digest()
);
char[] passwordChars = password.toCharArray();
final byte[] pkcs12PasswordBytes =
PBEParametersGenerator.PKCS12PasswordToBytes(passwordChars);
pGen.init(pkcs12PasswordBytes, bSalt, ITERATIONS);
CBCBlockCipher aesCBC = new CBCBlockCipher(new AESEngine());
ParametersWithIV aesCBCParams =
(ParametersWithIV) pGen.generateDerivedParameters(128, 128);
aesCBC.init(true, aesCBCParams);
PaddedBufferedBlockCipher aesCipher =
new PaddedBufferedBlockCipher(aesCBC, new PKCS7Padding());
aesCipher.init(true, aesCBCParams);
byte[] buf = new byte[BUF_SIZE];
// Read in the decrypted bytes and write the cleartext to out
int numRead = 0;
while ((numRead = fin.read(buf)) >= 0) {
if (numRead == 1024) {
byte[] plainTemp = new byte[
aesCipher.getUpdateOutputSize(numRead)];
int offset =
aesCipher.processBytes(buf, 0, numRead, plainTemp, 0);
final byte[] plain = new byte[offset];
System.arraycopy(plainTemp, 0, plain, 0, plain.length);
fout.write(plain, 0, plain.length);
} else {
byte[] plainTemp = new byte[aesCipher.getOutputSize(numRead)];
int offset =
aesCipher.processBytes(buf, 0, numRead, plainTemp, 0);
int last = aesCipher.doFinal(plainTemp, offset);
final byte[] plain = new byte[offset + last];
System.arraycopy(plainTemp, 0, plain, 0, plain.length);
fout.write(plain, 0, plain.length);
}
}
fout.close();
fin.close();
} catch (Exception e) {
e.printStackTrace();
}
}
private static void decrypt(InputStream fin,
OutputStream fout,
String password,
byte[] bSalt) {
try {
PKCS12ParametersGenerator pGen = new PKCS12ParametersGenerator(
new SHA256Digest()
);
char[] passwordChars = password.toCharArray();
final byte[] pkcs12PasswordBytes =
PBEParametersGenerator.PKCS12PasswordToBytes(passwordChars);
pGen.init(pkcs12PasswordBytes, bSalt, ITERATIONS);
CBCBlockCipher aesCBC = new CBCBlockCipher(new AESEngine());
ParametersWithIV aesCBCParams =
(ParametersWithIV) pGen.generateDerivedParameters(128, 128);
aesCBC.init(false, aesCBCParams);
PaddedBufferedBlockCipher aesCipher =
new PaddedBufferedBlockCipher(aesCBC, new PKCS7Padding());
aesCipher.init(false, aesCBCParams);
byte[] buf = new byte[BUF_SIZE];
// Read in the decrypted bytes and write the cleartext to out
int numRead = 0;
while ((numRead = fin.read(buf)) >= 0) {
if (numRead == 1024) {
byte[] plainTemp = new byte[
aesCipher.getUpdateOutputSize(numRead)];
int offset =
aesCipher.processBytes(buf, 0, numRead, plainTemp, 0);
// int last = aesCipher.doFinal(plainTemp, offset);
final byte[] plain = new byte[offset];
System.arraycopy(plainTemp, 0, plain, 0, plain.length);
fout.write(plain, 0, plain.length);
} else {
byte[] plainTemp = new byte[
aesCipher.getOutputSize(numRead)];
int offset =
aesCipher.processBytes(buf, 0, numRead, plainTemp, 0);
int last = aesCipher.doFinal(plainTemp, offset);
final byte[] plain = new byte[offset + last];
System.arraycopy(plainTemp, 0, plain, 0, plain.length);
fout.write(plain, 0, plain.length);
}
}
fout.close();
fin.close();
} catch (Exception e) {
e.printStackTrace();
}
}
However under iOS 4.2 (Working with XCode) I cannot figure out how to do the equivalent,
This is what I have tried under Objective C, with the goal of decrypting data from the Android side, stored in mysql database, to test this out:
+(NSData*) decrypt:(NSData*)cipherData
userPassword:(NSString*)argPassword
genSalt:(NSData*)argPtrSalt{
size_t szPlainBufLen = cipherData.length + (kCCBlockSizeAES128);
uint8_t *ptrPlainBuf = malloc(szPlainBufLen);
//
const unsigned char *ptrPasswd =
(const unsigned char*)[argPassword
cStringUsingEncoding:NSASCIIStringEncoding];
int ptrPasswdLen = strlen(ptrPasswd);
//
NSString *ptrSaltStr = [[NSString alloc]
initWithData:argPtrSalt
encoding:NSASCIIStringEncoding];
const unsigned char *ptrSalt =
(const unsigned char *)[ptrSaltStr UTF8String];
NSString *ptrCipherStr =
[[NSString alloc]initWithData:cipherData
encoding:NSASCIIStringEncoding];
unsigned char *ptrCipher = (unsigned char *)[ptrCipherStr UTF8String];
unsigned char key[kCCKeySizeAES128];
unsigned char iv[kCCKeySizeAES128];
//
//int EVP_BytesToKey(const EVP_CIPHER *type,const EVP_MD *md,
//const unsigned char *salt, const unsigned char *data,
//int datal, int count, unsigned char *key,unsigned char *iv);
int i = EVP_BytesToKey(EVP_aes_128_cbc(),
EVP_sha256(),
ptrSalt,
ptrPasswd,
ptrPasswdLen,
PBKDF2_ITERATIONS,
key,
iv);
NSAssert(i == kCCKeySizeAES128,
@"Unable to generate key for AES");
//
size_t cipherLen = [cipherData length];
size_t outlength = 0;
//
CCCryptorStatus resultCCStatus = CCCrypt(kCCDecrypt,
kCCAlgorithmAES128,
kCCOptionPKCS7Padding,
key,
kCCBlockSizeAES128,
iv,
ptrCipher,
cipherLen,
ptrPlainBuf,
szPlainBufLen,
&outlength);
NSAssert(resultCCStatus == kCCSuccess,
@"Unable to perform PBE AES128bit decryption: %d", errno);
NSData *ns_dta_PlainData = nil;
if (resultCCStatus == kCCSuccess){
ns_dta_PlainData =
[NSData dataWithBytesNoCopy:ptrPlainBuf length:outlength];
}else{
return nil;
}
return ns_dta_PlainData;
}
Have supplied the data and user's password and get a return code from CCCrypt
as -4304
which indicates not successful and bad decoding.
I have thought that perhaps the encoding scheme would be throwing off the CommonCryptor's decryption routing hence the long-winded way of converting to NSASCIIStringEncoding
.
The Salt is stored along with the cipher data, and is 32bytes in length.
What am I missing in this regard, bearing in mind, am weak on cryptography.