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

Question

我正在为ios和Android开发应用程序。 我对加密任务比较陌生，在过去的3天里，我不停地撞墙，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我有（显然，因为它几乎与服务器端的代码相同）没有麻烦，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中的做法：

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（不正常工作）ios代码，从这里借来的：

http://blog.wingsofhermes.org/?p=75和苹果加密练习。

-(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，我试图仅加密长度为4个字节的输入。 这应该小到足以适合一个街区。 公钥导入和加密过程似乎有效，但与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并且在java中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ios/objc强制执行相同的行为？

Answer 1

尝试将密文分成多个部分，以便每个部分包含16个字符长并分别解码它们。 我也遇到了同样的问题，但是在PHP中存在了很长时间，而且上面的技巧对我有用。

这可能有助于您摆脱问题。

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

通过IOS代码，您可以看到它正在解析DER编码的ASN.1。 它正确识别前两个SEQUENCE标记，并跳过OID字段，甚至不验证它是否为OID。 然后出现问题：IOS代码期望下一个标记为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。 如果没有NULL，我们会看到IOS代码已经成功提取了BITSTRING的内容。

所以：NULL是一个可选字段，IOS代码不允许它，或者IOS代码期望不同的ASN.1结构。 例如，看起来BITSTRING也是DER编码的ASN.1 INTEGER（可能是RSA模数）。 然而IOS代码没有尝试解析它。 可能是IOS SecKeyEncrypt例程期望模数的这种格式，或者可能是调用者应该提取模数的原始字节。

所以仍然需要一些实验。 但是，如果此代码要解析提供的数据对象，则必须使用以下附加条件：

/* 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的ASN.1格式，在外部世界（客户端，服务器端）可以正常工作，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格式使它们可行。