AESCrypt encryption/decryption from PHP to iOS - php

Question

I need to convert the encryption/decryption method follows in our server side, please check the below code
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$iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
$iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
$key = "a16byteslongkey!";
$plaintext = "iphone";
$ciphertext = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key, $plaintext, MCRYPT_MODE_CBC, $iv);
$ciphertext = base64_encode($ciphertext);
echo "ciphertext: ".$ciphertext."<br/>";
$ciphertextinput = base64_decode($ciphertext);
$cipherdetext = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key, $ciphertextinput, MCRYPT_MODE_CBC, $iv);
echo "decryptText:".$cipherdetext."<br/>";
I tried with AES 256 encryption but it gives different results,
Encryption
- (NSData *)AES256EncryptWithKey:(NSString *)key {
// 'key' should be 32 bytes for AES256, will be null-padded otherwise
char keyPtr[kCCKeySizeAES256+1]; // room for terminator (unused)
bzero(keyPtr, sizeof(keyPtr)); // fill with zeroes (for padding)
// fetch key data
[key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
NSUInteger dataLength = [self length];
//See the doc: For block ciphers, the output size will always be less than or
//equal to the input size plus the size of one block.
//That's why we need to add the size of one block here
size_t bufferSize = dataLength + kCCBlockSizeAES128;
void *buffer = malloc(bufferSize);
size_t numBytesEncrypted = 0;
CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding,
keyPtr, kCCKeySizeAES256,
NULL /* initialization vector (optional) */,
[self bytes], dataLength, /* input */
buffer, bufferSize, /* output */
&numBytesEncrypted);
if (cryptStatus == kCCSuccess) {
//the returned NSData takes ownership of the buffer and will free it on deallocation
return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
}
free(buffer); //free the buffer;
return nil;}
Decryption
- (NSData *)AES256DecryptWithKey:(NSString *)key {
// 'key' should be 32 bytes for AES256, will be null-padded otherwise
char keyPtr[kCCKeySizeAES256+1]; // room for terminator (unused)
bzero(keyPtr, sizeof(keyPtr)); // fill with zeroes (for padding)
// fetch key data
[key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
char ivPtr = "";
NSUInteger dataLength = [self length];
//See the doc: For block ciphers, the output size will always be less than or
//equal to the input size plus the size of one block.
//That's why we need to add the size of one block here
size_t bufferSize = dataLength + kCCBlockSizeAES128;
void *buffer = malloc(bufferSize);
size_t numBytesDecrypted = 0;
CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding,
keyPtr, kCCKeySizeAES256,
NULL /* initialization vector (optional) */,
[self bytes], dataLength, /* input */
buffer, bufferSize, /* output */
&numBytesDecrypted);
if (cryptStatus == kCCSuccess) {
//the returned NSData takes ownership of the buffer and will free it on deallocation
return [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted];
}
free(buffer); //free the buffer;
return nil;}
OriginalText: iphone
ciphertext: SXNepKfh0IrlDDdkq4EdmQ==
Whats wrong here, Please give some suggestion for decrypt encrypted text from PHP. How to get exact "iphone" word from base 64 encode string SXNepKfh0IrlDDdkq4EdmQ==
Also, Please let me know how to use ECB Mode in AES encryption.
Thanks!

Answer 1

The problem:
`mcrypt uses non-standard null data padding, the iOS code is using PKCS#7 padding.
The fix, three choices:
Use PKCS#7 padding, for mcrypt add PKCS#7 padding the prior to encryption and remove it after decryption. (recommended)
or
Use null padding, for Common Crypto do not specify kCCOptionPKCS7Padding, add null padding prior to encryption and remove after decryption. (not recommended)
or
It is best not to use mcrypt, it is abandonware, has not been updated in years and does not support standard PKCS#7 (née PKCS#5) padding, only non-standard null padding that can't even be used with binary data. mcrypt has many outstanding bugs dating back to 2003. The mcrypt-extension is deprecated will be removed in PHP 7.2. Instead consider using defuse or RNCryptor, they provide a complete solution and are being maintained and is correct.