java - Android Java - 使用 RSA 公钥 .PEM 加密字符串

Question

我有一个 RSA 公钥证书。我可以使用具有 .PEM 扩展名的文件或简单地将其用作具有以下格式的字符串:

-----开始RSA公钥-----

{KEY}

-----结束RSA公钥-----

我正在尝试使用此 key 将加密的 JSON 发送到服务器。我尝试了其他相关堆栈溢出问题的多种解决方案，但没有一个答案不适合我。这个答案似乎有道理https://stackoverflow.com/a/43534042 ，但有些东西不能正常工作，根据其中一条评论，可能是因为 X509EncodedKeySpec 期望 DER 编码数据而不是 PEM。但在这种情况下，我应该为 PEM 编码数据使用什么？

Answer 1

正如@Topaco 已经评论过的，您的 RSA 公钥采用 PEM 编码，但采用 PKCS#1 格式，而不是 Java 可读的 PKCS#8 格式“开箱即用”。

@Maarten Bodewes 在 SO ( https://stackoverflow.com/a/54246646/8166854 ) 上提供了以下解决方案，将完成读取并将其转换为 (Java) 可用 RSAPublicKey 的工作。

该解决方案在我的 OpenJdk11 上运行，如果您使用的是“Android Java”，您可能需要更改 Base64 调用。不需要像 Bouncy CaSTLe 这样的外部库。请遵守 Maarten 关于 key 长度的注释。

简单的输出:

Load RSA PKCS#1 Public Keys
pkcs1PublicKey: Sun RSA public key, 2048 bits
  params: null
  modulus: 30333480050529072539152474433261825229175303911986187056546130987160889422922632165228273249976997833741424393377152058709551313162877595353675051556949998681388601725684016724167050111037861889500002806879899578986908702627237884089998121288607696752162223715667435607286689842713475938751449494999920670300421827737208147069624343973533326291094315256948284968840679921633097541211738122424891429452073949806872319418453594822983237338545978675594260211082913078702997218079517998196340177653632261614031770091082266225991043014081642881957716572923856737534043425399435601282335538921977379429228634484095086075971
  public exponent: 65537

代码:

import java.io.IOException;
import java.security.GeneralSecurityException;
import java.security.KeyFactory;
import java.security.NoSuchAlgorithmException;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.X509EncodedKeySpec;
import java.util.Base64;

public class LoadPkcs1PublicKeyPemSo {
    // solution from https://stackoverflow.com/a/54246646/8166854  answered Jan 18 '19 at 1:36 Maarten Bodewes
    private static final int SEQUENCE_TAG = 0x30;
    private static final int BIT_STRING_TAG = 0x03;
    private static final byte[] NO_UNUSED_BITS = new byte[] { 0x00 };
    private static final byte[] RSA_ALGORITHM_IDENTIFIER_SEQUENCE =
            {(byte) 0x30, (byte) 0x0d,
                    (byte) 0x06, (byte) 0x09, (byte) 0x2a, (byte) 0x86, (byte) 0x48, (byte) 0x86, (byte) 0xf7, (byte) 0x0d, (byte) 0x01, (byte) 0x01, (byte) 0x01,
                    (byte) 0x05, (byte) 0x00};

    public static void main(String[] args) throws GeneralSecurityException, IOException {
        System.out.println("Load RSA PKCS#1 Public Keys");

        String rsaPublicKeyPem = "-----BEGIN RSA PUBLIC KEY-----\n" +
                "MIIBCgKCAQEA8EmWJUZ/Osz4vXtUU2S+0M4BP9+s423gjMjoX+qP1iCnlcRcFWxt\n" +
                "hQGN2CWSMZwR/vY9V0un/nsIxhZSWOH9iKzqUtZD4jt35jqOTeJ3PCSr48JirVDN\n" +
                "Let7hRT37Ovfu5iieMN7ZNpkjeIG/CfT/QQl7R+kO/EnTmL3QjLKQNV/HhEbHS2/\n" +
                "44x7PPoHqSqkOvl8GW0qtL39gTLWgAe801/w5PmcQ38CKG0oT2gdJmJqIxNmAEHk\n" +
                "atYGHcMDtXRBpOhOSdraFj6SmPyHEmLBishaq7Jm8NPPNK9QcEQ3q+ERa5M6eM72\n" +
                "PpF93g2p5cjKgyzzfoIV09Zb/LJ2aW2gQwIDAQAB\n" +
                "-----END RSA PUBLIC KEY-----";

        RSAPublicKey pkcs1PublicKey = getPkcs1PublicKeyFromString(rsaPublicKeyPem);
        System.out.println("pkcs1PublicKey: " + pkcs1PublicKey);
    }

    public static RSAPublicKey getPkcs1PublicKeyFromString(String key) throws GeneralSecurityException {
        String publicKeyPEM = key;
        publicKeyPEM = publicKeyPEM.replace("-----BEGIN RSA PUBLIC KEY-----", "");
        publicKeyPEM = publicKeyPEM.replace("-----END RSA PUBLIC KEY-----", "");
        publicKeyPEM = publicKeyPEM.replaceAll("[\\r\\n]+", "");
        byte[] pkcs1PublicKeyEncoding = Base64.getDecoder().decode(publicKeyPEM);
        return decodePKCS1PublicKey(pkcs1PublicKeyEncoding);
    }

/*
solution from https://stackoverflow.com/a/54246646/8166854  answered Jan 18 '19 at 1:36 Maarten Bodewes
The following code turns a PKCS#1 encoded public key into a SubjectPublicKeyInfo encoded public key,
which is the public key encoding accepted by the RSA KeyFactory using X509EncodedKeySpec -
as SubjectPublicKeyInfo is defined in the X.509 specifications.

Basically it is a low level DER encoding scheme which
    wraps the PKCS#1 encoded key into a bit string (tag 0x03, and a encoding for the number of unused
    bits, a byte valued 0x00);
    adds the RSA algorithm identifier sequence (the RSA OID + a null parameter) in front -
    pre-encoded as byte array constant;
    and finally puts both of those into a sequence (tag 0x30).

No libraries are used. Actually, for createSubjectPublicKeyInfoEncoding, no import statements are even required.

Notes:

    NoSuchAlgorithmException should probably be caught and put into a RuntimeException;
    the private method createDERLengthEncoding should probably not accept negative sizes.
    Larger keys have not been tested, please validate createDERLengthEncoding for those -
    I presume it works, but better be safe than sorry.
*/

    public static RSAPublicKey decodePKCS1PublicKey(byte[] pkcs1PublicKeyEncoding)
            throws NoSuchAlgorithmException, InvalidKeySpecException
    {
        byte[] subjectPublicKeyInfo2 = createSubjectPublicKeyInfoEncoding(pkcs1PublicKeyEncoding);
        KeyFactory rsaKeyFactory = KeyFactory.getInstance("RSA");
        RSAPublicKey generatePublic = (RSAPublicKey) rsaKeyFactory.generatePublic(new X509EncodedKeySpec(subjectPublicKeyInfo2));
        return generatePublic;
    }

    public static byte[] createSubjectPublicKeyInfoEncoding(byte[] pkcs1PublicKeyEncoding)
    {
        byte[] subjectPublicKeyBitString = createDEREncoding(BIT_STRING_TAG, concat(NO_UNUSED_BITS, pkcs1PublicKeyEncoding));
        byte[] subjectPublicKeyInfoValue = concat(RSA_ALGORITHM_IDENTIFIER_SEQUENCE, subjectPublicKeyBitString);
        byte[] subjectPublicKeyInfoSequence = createDEREncoding(SEQUENCE_TAG, subjectPublicKeyInfoValue);
        return subjectPublicKeyInfoSequence;
    }

    private static byte[] concat(byte[] ... bas)
    {
        int len = 0;
        for (int i = 0; i < bas.length; i++)
        {
            len += bas[i].length;
        }
        byte[] buf = new byte[len];
        int off = 0;
        for (int i = 0; i < bas.length; i++)
        {
            System.arraycopy(bas[i], 0, buf, off, bas[i].length);
            off += bas[i].length;
        }
        return buf;
    }

    private static byte[] createDEREncoding(int tag, byte[] value)
    {
        if (tag < 0 || tag >= 0xFF)
        {
            throw new IllegalArgumentException("Currently only single byte tags supported");
        }
        byte[] lengthEncoding = createDERLengthEncoding(value.length);
        int size = 1 + lengthEncoding.length + value.length;
        byte[] derEncodingBuf = new byte[size];
        int off = 0;
        derEncodingBuf[off++] = (byte) tag;
        System.arraycopy(lengthEncoding, 0, derEncodingBuf, off, lengthEncoding.length);
        off += lengthEncoding.length;
        System.arraycopy(value, 0, derEncodingBuf, off, value.length);
        return derEncodingBuf;
    }

    private static byte[] createDERLengthEncoding(int size)
    {
        if (size <= 0x7F)
        {
            // single byte length encoding
            return new byte[] { (byte) size };
        }
        else if (size <= 0xFF)
        {
            // double byte length encoding
            return new byte[] { (byte) 0x81, (byte) size };
        }
        else if (size <= 0xFFFF)
        {
            // triple byte length encoding
            return new byte[] { (byte) 0x82, (byte) (size >> Byte.SIZE), (byte) size };
        }
        throw new IllegalArgumentException("size too large, only up to 64KiB length encoding supported: " + size);
    }
}