AES 128 encryption give special charcter - php

Question

I am trying to do AES128 encryption with key and iv and then convert into hex string.My problem is that when I encrypt string into aes128 and convert into hex it give me a hex string.but when i try this same thing in php I am getting diffrent hex string.So when I try to decrypt php hex string, its decrypted successfully. But when I try to decrypt my hex string in php it's give me special characters.
NSString *str = #"hello";
NSString *key = #"1234abcd5678abcd1234abcd5678abcd";
NSString *IV = #"1234567812345678";
NSData* data = [str dataUsingEncoding:NSUTF8StringEncoding];
NSData* responseData = [data AES128EncryptedDataWithKey:key iv:IV];
NSLog(#"%#",[self hexRepresentationWithSpaces_AS:NO withdata:responseData]);
- (NSData *)AES128Operation:(CCOperation)operation key:(NSString *)key iv:(NSString *)iv
{
char keyPtr[kCCKeySizeAES128 + 1];
bzero(keyPtr, sizeof(keyPtr));
[key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
char ivPtr[kCCBlockSizeAES128 + 1];
bzero(ivPtr, sizeof(ivPtr));
if (iv) {
[iv getCString:ivPtr maxLength:sizeof(ivPtr) encoding:NSUTF8StringEncoding];
}
NSUInteger dataLength = [self length];
size_t bufferSize = dataLength + kCCBlockSizeAES128;
void *buffer = malloc(bufferSize);
size_t numBytesEncrypted = 0;
CCCryptorStatus cryptStatus = CCCrypt(operation,
kCCAlgorithmAES,
kCCOptionPKCS7Padding,
keyPtr,
kCCBlockSizeAES128,
ivPtr,
[self bytes],
dataLength,
buffer,
bufferSize,
&numBytesEncrypted);
if (cryptStatus == kCCSuccess) {
return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
}
free(buffer);
return nil;
}
-(NSString*)hexRepresentationWithSpaces_AS:(BOOL)spaces withdata:(NSData*)data
{
const unsigned char* bytes = (const unsigned char*)[data bytes];
NSUInteger nbBytes = [data length];
//If spaces is true, insert a space every this many input bytes (twice this many output characters).
static const NSUInteger spaceEveryThisManyBytes = 4UL;
//If spaces is true, insert a line-break instead of a space every this many spaces.
static const NSUInteger lineBreakEveryThisManySpaces = 4UL;
const NSUInteger lineBreakEveryThisManyBytes = spaceEveryThisManyBytes * lineBreakEveryThisManySpaces;
NSUInteger strLen = 2*nbBytes + (spaces ? nbBytes/spaceEveryThisManyBytes : 0);
NSMutableString* hex = [[NSMutableString alloc] initWithCapacity:strLen];
for(NSUInteger i=0; i<nbBytes; ) {
[hex appendFormat:#"%02X", bytes[i]];
//We need to increment here so that the every-n-bytes computations are right.
++i;
if (spaces) {
if (i % lineBreakEveryThisManyBytes == 0) [hex appendString:#"\n"];
else if (i % spaceEveryThisManyBytes == 0) [hex appendString:#" "];
}
}
return hex ;
}
and In php I am using
$td = mcrypt_module_open('rijndael-128', '', 'cbc', $iv);
mcrypt_generic_init($td, $key, $iv);
$encrypted = mcrypt_generic($td, $str);
mcrypt_generic_deinit($td);
// mcrypt_module_close($td);
echo $hexdata = bin2hex($encrypted);
echo "<br>";
$bindata = '';
for ($i = 0; $i < strlen($hexdata); $i += 2) {
$bindata .= chr(hexdec(substr($hexdata, $i, 2)));
}
echo $bindata;
echo "<br>";
mcrypt_generic_init($td, $key, $iv);
$decrypted = mdecrypt_generic($td,$encrypted);
mcrypt_generic_deinit($td);
echo "encrypted : ".$encrypted;
echo "<br>";
echo "decrypted : ".$decrypted;

Answer 1

mcrypt is a very old library that does not even implement PKCS#7 compatible padding, which you are obviously using in your iOS code. So at the end you are left with a character representation of the padding, which will probably replaced with replacement characters.
A wrong IV will result in 16 characters being wrong, a wrong key in all characters being wrong. You may also want to match the UTF-8 encoding to be able to display characters with a code point above 0x7F.