如何从Java生成ssh兼容的id\u rsa(.pub)

ssh使用的密钥格式在 RFC #4253 . RSA公钥的格式如下:

  string    "ssh-rsa"
  mpint     e /* key public exponent */
  mpint     n /* key modulus */

所有数据类型编码都在的第5节中定义 RFC #4251 . 字符串和mpint(多精度整数)类型的编码方式如下:

  4-bytes word: data length (unsigned big-endian 32 bits integer)
  n bytes     : binary representation of the data

  byte[] data = new byte[] {0, 0, 0, 7, 's', 's', 'h', '-', 'r', 's', 'a'};

为公众编码:

   public byte[] encodePublicKey(RSAPublicKey key) throws IOException
   {
       ByteArrayOutputStream out = new ByteArrayOutputStream();
       /* encode the "ssh-rsa" string */
       byte[] sshrsa = new byte[] {0, 0, 0, 7, 's', 's', 'h', '-', 'r', 's', 'a'};
       out.write(sshrsa);
       /* Encode the public exponent */
       BigInteger e = key.getPublicExponent();
       byte[] data = e.toByteArray();
       encodeUInt32(data.length, out);
       out.write(data);
       /* Encode the modulus */
       BigInteger m = key.getModulus();
       data = m.toByteArray();
       encodeUInt32(data.length, out);
       out.write(data);
       return out.toByteArray();
   }

   public void encodeUInt32(int value, OutputStream out) throws IOException
   {
       byte[] tmp = new byte[4];
       tmp[0] = (byte)((value >>> 24) & 0xff);
       tmp[1] = (byte)((value >>> 16) & 0xff);
       tmp[2] = (byte)((value >>> 8) & 0xff);
       tmp[3] = (byte)(value & 0xff);
       out.write(tmp);
   }

对于私钥编码,有两种情况:

1. 私钥不受密码保护。在这种情况下,私钥根据PKCS#8标准进行编码,然后使用Base64进行编码。可以通过调用 getEncoded 在 RSAPrivateKey .
2. 私钥受密码保护。在这种情况下,密钥编码是OpenSSH专用格式。我不知道是否有这种格式的文档(当然除了OpenSSH源代码)

正如Carsten所提到的,JSch可以很容易地生成这些密钥对。 参考它的例子, KeyGen.java

gotoalberto 的 answer (以下引用)对于不同的问题,RSA和DSA密钥都适用:

如果你想反转这个过程,也就是编码一个 PublicKey Java对象 到Linux authorized_keys 输入格式,可以使用以下代码:

    /**
     * Encode PublicKey (DSA or RSA encoded) to authorized_keys like string
     *
     * @param publicKey DSA or RSA encoded
     * @param user username for output authorized_keys like string
     * @return authorized_keys like string
     * @throws IOException
     */
    public static String encodePublicKey(PublicKey publicKey, String user)
            throws IOException {
        String publicKeyEncoded;
        if(publicKey.getAlgorithm().equals("RSA")){
            RSAPublicKey rsaPublicKey = (RSAPublicKey) publicKey;
            ByteArrayOutputStream byteOs = new ByteArrayOutputStream();
            DataOutputStream dos = new DataOutputStream(byteOs);
            dos.writeInt("ssh-rsa".getBytes().length);
            dos.write("ssh-rsa".getBytes());
            dos.writeInt(rsaPublicKey.getPublicExponent().toByteArray().length);
            dos.write(rsaPublicKey.getPublicExponent().toByteArray());
            dos.writeInt(rsaPublicKey.getModulus().toByteArray().length);
            dos.write(rsaPublicKey.getModulus().toByteArray());
            publicKeyEncoded = new String(
                    Base64.encodeBase64(byteOs.toByteArray()));
            return "ssh-rsa " + publicKeyEncoded + " " + user;
        }
        else if(publicKey.getAlgorithm().equals("DSA")){
            DSAPublicKey dsaPublicKey = (DSAPublicKey) publicKey;
            DSAParams dsaParams = dsaPublicKey.getParams();

            ByteArrayOutputStream byteOs = new ByteArrayOutputStream();
            DataOutputStream dos = new DataOutputStream(byteOs);
            dos.writeInt("ssh-dss".getBytes().length);
            dos.write("ssh-dss".getBytes());
            dos.writeInt(dsaParams.getP().toByteArray().length);
            dos.write(dsaParams.getP().toByteArray());
            dos.writeInt(dsaParams.getQ().toByteArray().length);
            dos.write(dsaParams.getQ().toByteArray());
            dos.writeInt(dsaParams.getG().toByteArray().length);
            dos.write(dsaParams.getG().toByteArray());
            dos.writeInt(dsaPublicKey.getY().toByteArray().length);
            dos.write(dsaPublicKey.getY().toByteArray());
            publicKeyEncoded = new String(
                    Base64.encodeBase64(byteOs.toByteArray()));
            return "ssh-dss " + publicKeyEncoded + " " + user;
        }
        else{
            throw new IllegalArgumentException(
                    "Unknown public key encoding: " + publicKey.getAlgorithm());
        }
    }

任何问题的通用解决方案 PublicKey 类型(RSA、DSA等)是一个使用SSHJ的一行程序:

byte[] b = new Buffer.PlainBuffer().putPublicKey(key).getCompactData()

Base64.getEncoder().encodeToString(b) .