Question

I need to translate this into Objective-C, can anyone help ?

var randomString = "abc";
var computedHash = Convert.ToBase64String(new MD5CryptoServiceProvider().ComputeHash(Encoding.Default.GetBytes(computedValue)));

What is happening here first ?

I thought it was:

1. get bytes data from the randomString
2. MD5 that
3. Convert the result into data
4. Convert that data into a base 64 string.

This is what I got so far:

NSString    * completeString    = @"abc";
NSData      * bytes             = [completeString dataUsingEncoding:NSUTF8StringEncoding];
NSString    * md5ed             = [bytes md5];
NSData      * data               = [md5ed dataUsingEncoding:NSUnicodeStringEncoding];
NSString    * base64            = [NSString base64StringFromData:data length:[data length]];

I am using a category to generate the MD5 hash.

@implementation NSData (Crypto)

-(NSString*)md5{
    const char *cStr = [self bytes];
    unsigned char digest[CC_MD5_DIGEST_LENGTH];
    CC_MD5( cStr, [self length], digest );
    NSString* s = [NSString stringWithFormat: @"%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x",
                   digest[0], digest[1], 
                   digest[2], digest[3],
                   digest[4], digest[5],
                   digest[6], digest[7],
                   digest[8], digest[9],
                   digest[10], digest[11],
                   digest[12], digest[13],
                   digest[14], digest[15]];
    return s;

}

@end

Answer 1

I don’t know anything about Objective C, but Encoding.Default.GetBytes() returns the string encoded using UTF-16. And from the name, it seems NSUTF8StringEncoding uses UTF-8.

So, to get the same results as in C#, you need to get the string encoded as UTF-16.