iPhone开发技巧之数据篇（2）— iPhone程序中的加密处理

博主：易飞扬
原文链接 : http://www.yifeiyang.net/iphone-development-techniques-of-data-papers-2-iphone-encryption-program/

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CCCrypt base64encoding

iPhone开发技巧之数据篇（2）— iPhone程序中的加密处理

CCCrypt

在Objective-C语言中，加密时常用到CCCrypt(3cc) Mac OS X Manual Page。下面的代码使用 CCCrypt() ，给 NSData 类增加了 AES256EncryptWithKey, AES256DecryptWithKey 方法。

#import <CommonCrypto/CommonCryptor.h>

@implementation NSData (Additions)

@class NSString;

- (NSData *)AES256EncryptWithKey:(NSString *)key {
        char keyPtr[kCCKeySizeAES256+1];
        bzero(keyPtr, sizeof(keyPtr));

        [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];

        NSUInteger dataLength = [self length];

        size_t bufferSize = dataLength + kCCBlockSizeAES128;
        void *buffer = malloc(bufferSize);

        size_t numBytesEncrypted = 0;
        CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128,
                                                                         kCCOptionPKCS7Padding | kCCOptionECBMode,
                                                                         keyPtr, kCCBlockSizeAES128,
                                                                         NULL,
                                                                         [self bytes], dataLength,
                                                                         buffer, bufferSize,
                                                                         &numBytesEncrypted);
        if (cryptStatus == kCCSuccess) {
                return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
        }
        free(buffer);
        return nil;
}

- (NSData *)AES256DecryptWithKey:(NSString *)key {
        char keyPtr[kCCKeySizeAES256+1];
        bzero(keyPtr, sizeof(keyPtr));

        [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];

        NSUInteger dataLength = [self length];

        size_t bufferSize = dataLength + kCCBlockSizeAES128;
        void *buffer = malloc(bufferSize);

        size_t numBytesDecrypted = 0;
        CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmAES128,
                                                                         kCCOptionPKCS7Padding | kCCOptionECBMode,
                                                                         keyPtr, kCCBlockSizeAES128,
                                                                         NULL,
                                                                         [self bytes], dataLength,
                                                                         buffer, bufferSize,
                                                                         &numBytesDecrypted);

        if (cryptStatus == kCCSuccess) {
                return [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted];
        }
        free(buffer);
        return nil;
}
@end

使用的时候就像使用NSData一样。

base64encoding

有的时候需要向服务器上传递base64加密的数据，这个时候我们就可以像下面，给 NSData 类追加newStringInBase64FromData 方法。

- (NSString *)newStringInBase64FromData {
        NSMutableString *dest = [[NSMutableString alloc] initWithString:@""];
        unsigned char * working = (unsigned char *)[self bytes];
        int srcLen = [self length];

        for (int i=0; i<srcLen; i += 3) {
                for (int nib=0; nib<4; nib++) {
                    int byt = (nib == 0)?0:nib-1;
                        int ix = (nib+1)*2;

                        if (i+byt >= srcLen) break;

                        unsigned char curr = ((working[i+byt] << (8-ix)) & 0x3F);

                        if (i+nib < srcLen) curr |= ((working[i+nib] >> ix) & 0x3F);

                        [dest appendFormat:@"%c", base64[curr]];
                }
        }
        return dest;
}

同样，使用的时候就像使用NSData一样。

最终的代码如下所示：

//
//  NSDataAdditions.h
//
//  Copyright 2010 __MyCompanyName__. All rights reserved.
//

#import <Foundation/Foundation.h>

@class NSString;

@interface NSData (Additions)

- (NSData *)AES256EncryptWithKey:(NSString *)key;
- (NSData *)AES256DecryptWithKey:(NSString *)key;
- (NSString *)newStringInBase64FromData;

@end

// -----------------------------------------------------------------------------------

//
//  NSDataAdditions.m
//
//  Copyright 2010 __MyCompanyName__. All rights reserved.
//

#import "NSDataAdditions.h"
#import <CommonCrypto/CommonCryptor.h>

static char base64[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

@implementation NSData (Additions)

@class NSString;

- (NSData *)AES256EncryptWithKey:(NSString *)key {
    char keyPtr[kCCKeySizeAES256+1];
    bzero(keyPtr, sizeof(keyPtr));

    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];

    NSUInteger dataLength = [self length];

    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);

    size_t numBytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128,
                                          kCCOptionPKCS7Padding | kCCOptionECBMode,
                                          keyPtr, kCCBlockSizeAES128,
                                          NULL,
                                          [self bytes], dataLength,
                                          buffer, bufferSize,
                                          &numBytesEncrypted);
    if (cryptStatus == kCCSuccess) {
        return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
    }

    free(buffer);
    return nil;
}

- (NSData *)AES256DecryptWithKey:(NSString *)key {
    char keyPtr[kCCKeySizeAES256+1];
    bzero(keyPtr, sizeof(keyPtr));

    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];

    NSUInteger dataLength = [self length];

    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);

    size_t numBytesDecrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmAES128,
                                          kCCOptionPKCS7Padding | kCCOptionECBMode,
                                          keyPtr, kCCBlockSizeAES128,
                                          NULL,
                                          [self bytes], dataLength,
                                          buffer, bufferSize,
                                          &numBytesDecrypted);

    if (cryptStatus == kCCSuccess) {
        return [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted];
    }

    free(buffer);
    return nil;
}

- (NSString *)newStringInBase64FromData {
    NSMutableString *dest = [[NSMutableString alloc] initWithString:@""];
    unsigned char * working = (unsigned char *)[self bytes];
    int srcLen = [self length];

    for (int i=0; i<srcLen; i += 3) {
        for (int nib=0; nib<4; nib++) {
            int byt = (nib == 0)?0:nib-1;
            int ix = (nib+1)*2;

            if (i+byt >= srcLen) break;

            unsigned char curr = ((working[i+byt] << (8-ix)) & 0x3F);

            if (i+nib < srcLen) curr |= ((working[i+nib] >> ix) & 0x3F);

            [dest appendFormat:@"%c", base64[curr]];
        }
    }

    return dest;
}

@end

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