NSString+Extension.h

//  NSString+Extension.h

@interface NSString (Extension)

+ (NSString *) getUUID;

+ (NSString *) sha1:(NSString *)input;

@end

NSString+Extension.m

//  NSString+Extension.m

#import "NSString+Extension.h"
#import <CommonCrypto/CommonDigest.h>

@implementation NSString (Extension)

+ (NSString *)getUUID {
	CFUUIDRef theUUID = CFUUIDCreate(NULL);
	CFStringRef string = CFUUIDCreateString(NULL, theUUID);
	CFRelease(theUUID);
	return [(NSString *)string autorelease];
}

+ (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;
}

@end

test.m

#import "NSString+Extension.h"

    //Get a random hash (Generated from CFUUID+sha1)
    NSString *hash = [NSString sha1:[NSString getUUID]];

    //Shorten the sha1
    NSString *short_random_id = [hash substringFromIndex:[hash length]-10];
    
    //Random uppercase / lowercase the id
    NSMutableString *random_id_final = [NSMutableString string];
    for (NSUInteger i = 0; i < [short_random_id length]; i++)
    {
        NSString *substring = [short_random_id substringWithRange:NSMakeRange(i, 1)];
        [random_id_final appendString:(rand() % 2) ? [substring lowercaseString] : [substring uppercaseString]];
    }
    

//Use random_id_final