PKCS1-padding/RSA 加密 ios objc 和 java 的区别

Question

我正在为 ios 和 Android 开发一个应用程序。我对加密任务比较陌生，在过去的 3 天里，我一直在碰壁，因为我无法运行 RSA 加密。

两个客户端都从 Java 服务器接收公钥。在 android 中我（显然，因为它与服务器端的代码几乎相同）没有问题，但 ios 部分似乎根本不兼容。我想用公钥加密一小段数据（aes 密钥），这就是我在 Java 中这样做的方式：

try {
    String publickey  = "MCwwDQYJKoZIhvcNAQEBBQADGwAwGAIRAK+dBpbOKw+1VKMWoFxjU6UCAwEAAQ==";
    byte[] bArr = Crypto.base64Decode(publicKey, false);
    KeyFactory keyFactory = KeyFactory.getInstance("RSA", "BC");
    EncodedKeySpec publicKeySpec = new X509EncodedKeySpec(publicKey);
    PublicKey publicKey = keyFactory.generatePublic(publicKeySpec);

    Cipher cipher = Cipher.getInstance("RSA/NONE/PKCS1Padding", "BC");
    cipher.init(1,publicKey);
    int cipherBlockSize = cipher.getBlockSize();
    ByteArrayOutputStream bArrOut = new ByteArrayOutputStream();
    bArrOut.flush();
    int pos = 0;
    Log.i("ContentBufferLength", contentBuffer.length+"");

    while (true) {
        if (cipherBlockSize > contentBuffer.length - pos) {
            cipherBlockSize = contentBuffer.length - pos;
        }
        Log.i("CipherBlockSize", cipherBlockSize+"");
        byte[] tmp = cipher.doFinal(contentBuffer, pos, cipherBlockSize);
        bArrOut.write(tmp);
        pos += cipherBlockSize;
        if (contentBuffer.length <= pos) {
            break;
        }
    }
    bArrOut.flush();
    encryptedBuffer = bArrOut.toByteArray();
    bArrOut.close();
} catch (Exception ex) {
    throw ex;
}

//  Log.i("Encrypted Buffer Length", encryptedBuffer.length+"");
return encryptedBuffer;

这是我的（不能正常工作的）ios代码，从这里借来的：

http://blog.wingsofhermes.org/?p=75 和苹果密码练习。

-(NSString* )encryptWithPublicKey:(NSString*)key input:(NSString*) input {
    const size_t BUFFER_SIZE =      16;
    const size_t CIPHER_BUFFER_SIZE = 16;
   //const uint32_t PADDING = kSecPaddingNone;
    const uint32_t PADDING = kSecPaddingPKCS1;

    static const UInt8 publicKeyIdentifier[] = "de.irgendwas.app";

    NSData *publicTag;

    publicTag = [[NSData alloc] initWithBytes:publicKeyIdentifier length:sizeof(publicKeyIdentifier)];

    NSMutableDictionary *publicKey2 = [[NSMutableDictionary alloc] init];
    [publicKey2 setObject:kSecClassKey forKey:kSecClass];
    [publicKey2 setObject:kSecAttrKeyTypeRSA forKey:kSecAttrKeyType];
    [publicKey2 setObject:publicTag forKey:kSecAttrApplicationTag];
    SecItemDelete((CFDictionaryRef)publicKey2);


    NSData *strippedPublicKeyData = [NSData dataFromBase64String:key];

    unsigned char * bytes = (unsigned char *)[strippedPublicKeyData bytes];
    size_t bytesLen = [strippedPublicKeyData length];

    size_t i = 0;
    if (bytes[i++] != 0x30)
        [Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];

    /* Skip size bytes */
    if (bytes[i] > 0x80)
        i += bytes[i] - 0x80 + 1;
    else
        i++;

    if (i >= bytesLen)
        [Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];

    if (bytes[i] != 0x30)
        [Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];

    /* Skip OID */
    i += 15;

    if (i >= bytesLen - 2)
        [Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];

    if (bytes[i++] != 0x03)
        [Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];

    /* Skip length and null */
    if (bytes[i] > 0x80)
        i += bytes[i] - 0x80 + 1;
    else
        i++;

    if (i >= bytesLen)
        [Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];

    if (bytes[i++] != 0x00)
        [Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];

    if (i >= bytesLen)
        [Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];

    strippedPublicKeyData = [NSData dataWithBytes:&bytes[i] length:bytesLen - i];

    DLog(@"X.509 Formatted Public Key bytes:\n%@",[strippedPublicKeyData description]);

    if (strippedPublicKeyData == nil)
        [Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];



    CFTypeRef persistKey = nil;
    [publicKey2 setObject:strippedPublicKeyData forKey:kSecValueData];
    [publicKey2 setObject: (kSecAttrKeyClassPublic) forKey:kSecAttrKeyClass];
    [publicKey2 setObject:[NSNumber numberWithBool:YES] forKey:kSecReturnPersistentRef];

    OSStatus secStatus = SecItemAdd((CFDictionaryRef)publicKey2, &persistKey);

    if (persistKey != nil) CFRelease(persistKey);

    if ((secStatus != noErr) && (secStatus != errSecDuplicateItem))
        [Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];

    SecKeyRef keyRef = nil;
    [publicKey2 removeObjectForKey:kSecValueData];
    [publicKey2 removeObjectForKey:kSecReturnPersistentRef];
    [publicKey2 setObject:[NSNumber numberWithBool:YES] forKey:kSecReturnRef];
    [publicKey2 setObject: kSecAttrKeyTypeRSA forKey:kSecAttrKeyType];

    SecItemCopyMatching((CFDictionaryRef)publicKey2,(CFTypeRef *)&keyRef);
    if (!keyRef)
    [Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];  

    uint8_t *plainBuffer;
    uint8_t *cipherBuffer;
    uint8_t *decryptedBuffer;


    const char inputString[] = "1234";
    int len = strlen(inputString);
    // TODO: this is a hack since i know inputString length will be less than BUFFER_SIZE
    if (len > BUFFER_SIZE) len = BUFFER_SIZE-1;
    plainBuffer = (uint8_t *)calloc(BUFFER_SIZE, sizeof(uint8_t));
    cipherBuffer = (uint8_t *)calloc(CIPHER_BUFFER_SIZE, sizeof(uint8_t));
    decryptedBuffer = (uint8_t *)calloc(BUFFER_SIZE, sizeof(uint8_t));

    strncpy( (char *)plainBuffer, inputString, len);

    size_t plainBufferSize = strlen((char *)plainBuffer);
    size_t cipherBufferSize = CIPHER_BUFFER_SIZE;

    NSLog(@"SecKeyGetBlockSize() public = %lu", SecKeyGetBlockSize(keyRef));
    //  Error handling
    // Encrypt using the public.
    OSStatus status = noErr;

    status = SecKeyEncrypt(keyRef,
                           PADDING,
                           plainBuffer,
                           plainBufferSize,
                           &cipherBuffer[0],
                           &cipherBufferSize
                           );
    NSLog(@"encryption result code: %ld (size: %lu)", status, cipherBufferSize);

    return [[[NSString stringWithFormat:@"%s",cipherBuffer] dataUsingEncoding:NSUTF8StringEncoding] base64EncodedString];
}

出于测试目的和简单性，目前我尝试仅加密长度为 4 个字节的输入。这应该足够小以容纳一个块。公钥导入和加密过程似乎有效，但是与 android 方法相比，我总是收到更长的输出。

到目前为止，我遇到的唯一区别是 SecKeyGetBlockSize returns 16 和 java cipher.blocksize 返回 5。我认为其他 11 个字节是为 pkcs1 填充保留的，但是如何在 @987654325 中强制执行相同的行为@?

Answer 1

尝试将密文拆分为多个部分，使每个部分包含 16 个字符长并分别对其进行解码。我也遇到了同样的问题，但这是在 PHP 中使用了很长时间，上面的技巧对我有用。

这可能会帮助您摆脱问题。

Answer 2

解码 Base64 密钥给出：

MCwwDQYJKoZIhvcNAQEBBQADGwAwGAIRAK+dBpbOKw+1VKMWoFxjU6UCAwEAAQ==
-> 302c300d06092a864886f70d0101010500031b003018021100af9d0696ce2b0fb554a316a05c6353a50203010001

将其解释为 DER 编码的 ASN.1，我们发现：

30(2c) //SEQUENCE
  30(0d)  //SEQUENCE
    06(09): 2a 86 48 86 f7 0d 01 01 01  //OID 1.2.840.113548.1.1.1 (RSA Encryption)
    05(00): //NULL                           
    03(1b): [00] 30 18 02 11 00 af 9d 06 96 ce 2b 0f b5 54 a3 16 a0 5c 63 53 a5 02 03 01 00 01 //BITSTRING

BITSTRING 似乎也包含 DER 编码的 ASN.1：

30(18) //SEQUENCE
  02(11): 00 af 9d 06 96 ce 2b 0f b5 54 a3 16 a0 5c 63 53 a5 02 03 01 00 01 //INTEGER

 = 0xaf9d0696ce2b0fb554a316a05c6353a50203010001

遍历 IOS 代码，可以看到它正在解析 DER 编码的 ASN.1。它正确识别了前两个 SEQUENCE 标记，并跳过了 OID 字段，甚至没有验证它是否是 OID。那么问题就出现了：IOS代码期望下一个标签是 BITSTRING(0x03)——但在我们的数据中，我们有一个额外的 NULL(0x05) 字段来表示公共指数是隐式的。 IOS 代码在遇到 0x05 标记时引发异常。如果 NULL 不存在，我们看到 IOS 代码将成功提取 BITSTRING 的内容。

所以：要么 NULL 是可选字段，并且 IOS 代码不允许它，要么 IOS 代码需要不同的 ASN.1 结构。例如，BITSTRING 似乎也是一个 DER 编码的 ASN.1 INTEGER（可能是 RSA 模数）。然而 IOS 代码并没有尝试解析它。可能是 IOS SecKeyEncrypt 例程需要这种模数格式，也可能是调用者应该提取模数的原始字节。

所以仍然需要进行一些实验。但是，如果此代码要解析提供的数据对象，则肯定需要以下附加条件：

/* Skip OID */
i += 15;

if (i >= bytesLen - 2)
    [Exception raise:FAILURE function:__PRETTY_FUNCTION__ line:__LINE__ description:@"Could not set public key."];

if (bytes[i] == 0x05)    /* This should handle the spurious ASN.1 NULL field */
    i += 2;

if (bytes[i++] != 0x03)

Answer 3

在 Android 或 Java 中，生成的密钥采用标准 ASN.1 格式，在外部世界（客户端、服务器端）中运行良好，但在 iOS 中，生成的密钥（公共、私有）采用原始格式，您必须将其转换为适当的 ASN.1 格式以使其可用。