在NSString中存储密码而不在内存中可读

- (NSString *)AES256EncryptWithKey:(NSString *)key {
    char keyPtr[kCCKeySizeAES256 + 1];
    bzero(keyPtr, sizeof(keyPtr));
    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];

    NSUInteger dataLength = [self lengthOfBytesUsingEncoding:NSUTF8StringEncoding];
    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);

    size_t numBytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding,
                                          keyPtr, kCCKeySizeAES256,
                                          NULL,
                                          [self UTF8String], dataLength,
                                          buffer, bufferSize,
                                          &numBytesEncrypted);

    if (cryptStatus == kCCSuccess) {
        return [NSString stringWithFormat:@"%@", [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted]];
    }

    free(buffer);
    return nil;
}

- (NSString *)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,
                                          keyPtr, kCCKeySizeAES256,
                                          NULL,
                                          [self bytes], dataLength,
                                          buffer, bufferSize,
                                          &numBytesDecrypted);

    if (cryptStatus == kCCSuccess) {
        return [[NSString alloc] initWithBytes:buffer length:numBytesDecrypted encoding:NSUTF8StringEncoding];
    }

    free(buffer);
    return nil;
}

NSString *password = @"password";
NSString *key = @"1234567890123456";

NSString *encryptedPassword = [password AES256EncryptWithKey:key];
NSString *decryptedPassword = [encryptedPassword AES256DecryptWithKey:key];