IOS: [NSString Hash] appears with the same hash value problem

Cause of the problem:

At least there is special circumstances for which this unreliability kicks in.

Comparing [a hash] and [b hash] of different nsstring is safe when:

• The strings ' length is shorter or equal to characters.
• [a length] is different to [b length].
• The concatinated first, middle, and last from characters of a differ to the concatinated components of b.

Otherwise every difference between the first and the middle chars, as well as every difference between the middle and t He last characters, is not used while producing the [NSString hash] value.

Workaround:

For my case, the solution is pretty easy. I made use of a SHA1 hash, which produced
A fingerprint from the whole string instead of pieces. I got mine inspired by
The SHA1 method of Saurabh Sharma

LANG:OBJC SHA1

• (NSString *) SHA1 {NSData *data = [Self dat Ausingencoding:nsutf8stringencoding]; Uint8 t digest[cc SHA1 Digest LENGTH];

  cc_sha1 (Data.bytes, Data.length, Digest);

  nsmutablestring *output = [nsmutablestring stringwithcapacity:cc SHA1 digest_length * 2];

  for (int i = 0; i < CC SHA1 digest_length; i++) {[Output appendformat:@ '%02x ', Digest[i]];}

  return output;}

The SHA1 is for the name of a cached file, and generated by giving the complete URL of the resource to be cached. Works Perfect. I already filed a pull request for

http://www.makebetterthings.com/iphone/how-to-get-md5-and-sha1-in-objective-c-ios-sdk/

Ps:

How to get MD5 and SHA1 in Objective C (IOS SDK)

Calculating the MD5 and SHA1 hash in IOS SDK are pretty simple-

Step 1 , haven very first thing you need to does is import Commoncrypto ' s CommonDigest.h

#import <CommonCrypto/CommonDigest.h>

Step 2 – Here is the real code for calculating SHA1 and MD5 hash-

SHA1-

-(nsstring*) SHA1: (nsstring*) input{const char *CSTR = [input cstringusingencoding:nsutf8stringencoding]; NSData *data = [NSData datawithbytes:cstr length:input.length]; uint8_t Digest[cc_sha1_digest_length]; CC_SHA1 (Data.bytes, Data.length, Digest); nsmutablestring* output = [nsmutablestring stringwithcapacity:cc_sha1_digest_length * 2]; for (int i = 0; i < cc_sha1_digest_length; i++) [Output appendformat:@ "%02x", Digest[i]]; return output;}

MD5-

-(NSString *) MD5: (NSString *) input{const char *CSTR = [input utf8string]; unsigned char digest[16]; CC_MD5 (CStr, strlen (CSTR), Digest); The MD5 call nsmutablestring *output = [nsmutablestring stringwithcapacity:cc_md5_digest_length * 2]; for (int i = 0; i < cc_md5_digest_length; i++) [Output appendformat:@ "%02x", Digest[i]]; return  output;}

Hope it would help someone!!

IOS: [NSString Hash] appears with the same hash value problem