how do i create a sha256 hash of a file(jpeg,pdf and tiff) using objective-c

Question

i used the following code that i took from here.

- (NSData *)sha256:(NSData *)data {

unsigned char hash[CC_SHA256_DIGEST_LENGTH];

if ( CC_SHA256([data bytes], [data length], hash) ) {

    NSData *sha256 = [NSData dataWithBytes:hash length:CC_SHA256_DIGEST_LENGTH];

    return sha256;
}
return nil;
}

NSData *imageHash=[self sha256:imageData];

imageHashtag =  [imageHash base64EncodedStringWithOptions:NSDataBase64Encoding64CharacterLineLength];

I am having some problems with this though- the hash being created includes / and = that are not supposed to be there. Can someone help me figure out the mistake i am making here? and how can i solve it?

edit: I found the possible problem- i was converting the sha hash that was an base64 encoded data back into another base64string. but when i used the following code to convert the hashdata into string, i only get nil. so can someone help me with converting the sha hash into a string?

imageHashtag = [NSString stringWithUTF8String:[imageHash bytes]];

the imagehash does have 32 bits of data, but imagehashtag is nil.

score 1 · Accepted Answer · answered Oct 08 '15 at 10:41

we added the following code to solve the problem:

    NSString *hash=[sha256 description];
    hash = [hash stringByReplacingOccurrencesOfString:@" " withString:@""];
    hash = [hash stringByReplacingOccurrencesOfString:@"<" withString:@""];
    hash = [hash stringByReplacingOccurrencesOfString:@">" withString:@""];

    return hash;

to solve our problem.

how do i create a sha256 hash of a file(jpeg,pdf and tiff) using objective-c

1 Answers1