NSString md5 hash category

NSString+Hash.h

#import <Foundation/Foundation.h>

@interface NSString (Hash)

- (NSString *)md5;

+ (NSString *)stringWithHash:(unsigned char *)hash
                digestLength:(int32_t)digestLength;

@end

NSString+Hash.m

#import "NSString+Hash.h"
#import <CommonCrypto/CommonCrypto.h>

@implementation NSString (Hash)

- (NSString *)md5 {
    const char * pointer = [self UTF8String];
    unsigned char md5Buffer[CC_MD5_DIGEST_LENGTH];
    
    CC_MD5(pointer, (CC_LONG)strlen(pointer), md5Buffer);
    
    return [NSString stringWithHash:md5Buffer digestLength:CC_MD5_DIGEST_LENGTH];
}

+ (NSString *)stringWithHash:(unsigned char *)hash
                digestLength:(int32_t)digestLength {
    
    NSMutableString *string = [NSMutableString stringWithCapacity:digestLength * 2];
    for (int i = 0; i < digestLength; i++) {
        [string appendFormat:@"%02x", hash[i]];
    }
    
    return [string copy];
}

@end