Get a string representation of your NSData with or without spaces or capitals

NSData+Hex.h

//
//  NSData+Hex.h
//
//  Based on code by AliSoftware
//  http://stackoverflow.com/a/7520723/60488
//

#import <Foundation/Foundation.h>

@interface NSData (Hex)

- (NSString *)hexRepresentationWithSpaces:(BOOL)spaces capitals:(BOOL)capitals;

@end

NSData+Hex.m

//
//  NSData+Hex.m
//
//  Based on code by AliSoftware
//  http://stackoverflow.com/a/7520723/60488
//

#import "NSData+Hex.h"

@implementation NSData (Hex)

- (NSString *)hexRepresentationWithSpaces:(BOOL)spaces capitals:(BOOL)capitals {
    const unsigned char *bytes = (const unsigned char *)[self bytes];
    NSUInteger nbBytes = [self length];
    // If spaces is true, insert a space every this many input bytes (twice this many output characters).
    static const NSUInteger spaceEveryThisManyBytes = 4UL;
    // If spaces is true, insert a line-break instead of a space every this many spaces.
    static const NSUInteger lineBreakEveryThisManySpaces = 4UL;
    const NSUInteger lineBreakEveryThisManyBytes = spaceEveryThisManyBytes * lineBreakEveryThisManySpaces;
    NSUInteger strLen = 2 * nbBytes + (spaces ? nbBytes / spaceEveryThisManyBytes : 0);

    NSMutableString *hex = [[NSMutableString alloc] initWithCapacity:strLen];

    for (NSUInteger i = 0; i < nbBytes; ) {
        if (capitals) {
            [hex appendFormat:@"%02X", bytes[i]];
        } else {
            [hex appendFormat:@"%02x", bytes[i]];
        }
        // We need to increment here so that the every-n-bytes computations are right.
        ++i;

        if (spaces) {
            if (i % lineBreakEveryThisManyBytes == 0) {
                [hex appendString:@"\n"];
            } else if (i % spaceEveryThisManyBytes == 0) {
                [hex appendString:@" "];
            }
        }
    }
    return [hex autorelease];
}

@end