在iOS開發中，為了數據的安全經常對內容進行加密，在這兒我們對常用的加密算法進行了總結：

1、MD5

+ (NSString *)md5Hash:(NSString *)str {
    const char *cStr = [str UTF8String];
    unsigned char result[16];
    CC_MD5( cStr, strlen(cStr), result );
    NSString *md5Result = [NSString stringWithFormat:
                           @"%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x",
                           result[0], result[1], result[2], result[3],
                           result[4], result[5], result[6], result[7],
                           result[8], result[9], result[10], result[11],
                           result[12], result[13], result[14], result[15]
                           ];
    return md5Result;
}

2. SHA1數字簽名算法

const char *cstr = [str cStringUsingEncoding:NSUTF8StringEncoding];
    NSData *data = [NSData dataWithBytes:cstr length:str.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;

3.AES加密算法

- (NSData *)AES256EncryptWithKey:(NSString *)key {//加密
    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 {//解密
    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;
}

4、BASE64編碼

+ (NSString*)encodeBase64String:(NSString * )input { 
    NSData *data = [input dataUsingEncoding:NSUTF8StringEncoding allowLossyConversion:YES]; 
    data = [GTMBase64 encodeData:data]; 
    NSString *base64String = [[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding] autorelease]; 
	return base64String;
}

+ (NSString*)decodeBase64String:(NSString * )input { 
    NSData *data = [input dataUsingEncoding:NSUTF8StringEncoding allowLossyConversion:YES]; 
    data = [GTMBase64 decodeData:data]; 
    NSString *base64String = [[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding] autorelease]; 
	return base64String;
} 

+ (NSString*)encodeBase64Data:(NSData *)data {
	data = [GTMBase64 encodeData:data]; 
    NSString *base64String = [[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding] autorelease];
	return base64String;
}

+ (NSString*)decodeBase64Data:(NSData *)data {
	data = [GTMBase64 decodeData:data]; 
    NSString *base64String = [[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding] autorelease];
	return base64String;
}