Question

I have some problems decrypting a file encrypted with openssl in a bash. Below is what I did step by step. I can’t figure out where does it go wrong.

The original file (ended with newline) :

123456
abcdef
ghijkl

Generate 32 bytes long random password :

$ openssl rand -hex 32
fec8950708098e9075e8b4df9a969aa7963c4d820158e965c7848dbfc8ca73ed

Encrypt the file :

$ openssl aes-128-ecb -in original.txt -out encrypted.txt

About the encrypted file :

$ file encrypted.txt
encrypted.txt: Non-ISO extended-ASCII text, with CR line terminators, with overstriking
$ cat encrypted.txt
Salted__??\z?F?z????4G}Q? Y?{ӌ???????b*??

Code to call the decrypt method :

NSData *myDataDec = [self aesDecrypt:@"fec8950708098e9075e8b4df9a969aa7963c4d820158e965c7848dbfc8ca73ed" data:myData];
NSLog(@"decrypted: %@", [[NSString alloc] initWithData:myDataDec encoding:NSASCIIStringEncoding]);

Method to decrypt :

- (NSData *)aesDecrypt:(NSString *)key data:(NSData *)data
{  

    // '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 = [data 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(kCCDecrypt, 
                                          kCCAlgorithmAES128, 
                                          kCCOptionPKCS7Padding,
                                          keyPtr, 
                                          kCCKeySizeAES256,
                                          NULL /* initialization vector (optional) */,             
                                          [data bytes], 
                                          dataLength, /* input */             
                                          buffer, 
                                          bufferSize, /* output */             
                                          &numBytesEncrypted);  
    NSLog(@"cryptStatus: %d", cryptStatus);
    if (cryptStatus == kCCSuccess) 
    {   
        NSLog(@"aes success");
        //the returned NSData takes ownership of the buffer and will free it on deallocation   
        return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];  
    }   
    NSLog(@"aes error");
    free(buffer); //free the buffer;  
    return nil; 
}

Logs :

2012-09-01 15:08:51.331 My Project[75582:f803] cryptStatus: -4304
2012-09-01 15:08:51.332 My Project[75582:f803] aes error
2012-09-01 15:08:51.332 My Project[75582:f803] decrypted:

kCCDecodeError details :

kCCDecodeError - Input data did not decode or decrypt properly.

Answer 1

OpenSSL uses a nonstandard format. AESencrypt is very broken (and insecure). Put them together and it’s not going to work. See RNCryptor for an OpenSSL-compatible solution on iOS. OpenSSL has a lot of problems itself, but it’s the best commandline option I can recommend right now.