Java ssh-rsa 字符串到公钥

Question

我想获取 .pub 文件内容的公钥。这是一个 .pub 文件内容的示例(使用 ssh-keygen 生成):

ssh-rsa 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 test@test.com

如果我是对的，这不是公钥，但可以从这个字符串中获取公钥。

这个答案回答了我的问题 https://stackoverflow.com/a/19387517/2735398
但答案似乎不起作用。我得到一个异常(exception):

java.security.spec.InvalidKeySpecException: java.security.InvalidKeyException: invalid key format

当查看答案的评论时，我不是唯一有问题的人......

如何修复异常？或者有其他方法从字符串中获取公钥吗？

Answer 1

这是我的 SSH RSA -> RSAPublicKey 转换器实现。我在网上的某个地方找到了 key 格式说明，非常感谢提供它的人。

public class CertificateUtils {
    private static final int VALUE_LENGTH = 4;
    private static final byte[] INITIAL_PREFIX = new byte[]{0x00, 0x00, 0x00, 0x07, 0x73, 0x73, 0x68, 0x2d, 0x72, 0x73, 0x61};
    private static final Pattern SSH_RSA_PATTERN = Pattern.compile("ssh-rsa[\\s]+([A-Za-z0-9/+]+=*)[\\s]+.*");

// SSH-RSA key format
//
//        00 00 00 07             The length in bytes of the next field
//        73 73 68 2d 72 73 61    The key type (ASCII encoding of "ssh-rsa")
//        00 00 00 03             The length in bytes of the public exponent
//        01 00 01                The public exponent (usually 65537, as here)
//        00 00 01 01             The length in bytes of the modulus (here, 257)
//        00 c3 a3...             The modulus

    public static RSAPublicKey parseSSHPublicKey(String key) throws InvalidKeyException {
        Matcher matcher = SSH_RSA_PATTERN.matcher(key.trim());
        if (!matcher.matches()) {
            throw new InvalidKeyException("Key format is invalid for SSH RSA.");
        }
        String keyStr = matcher.group(1);

        ByteArrayInputStream is = new ByteArrayInputStream(Base64.decodeBase64(keyStr));

        byte[] prefix = new byte[INITIAL_PREFIX.length];

        try {
            if (INITIAL_PREFIX.length != is.read(prefix) || !ArrayUtils.isEquals(INITIAL_PREFIX, prefix)) {
                throw new InvalidKeyException("Initial [ssh-rsa] key prefix missed.");
            }

            BigInteger exponent = getValue(is);
            BigInteger modulus = getValue(is);

            return (RSAPublicKey) KeyFactory.getInstance("RSA").generatePublic(new RSAPublicKeySpec(modulus, exponent));
        } catch (IOException | InvalidKeySpecException | NoSuchAlgorithmException e) {
            throw new InvalidKeyException("Failed to read SSH RSA certificate from string", e);
        }
    }

    private static BigInteger getValue(InputStream is) throws IOException {
        byte[] lenBuff = new byte[VALUE_LENGTH];
        if (VALUE_LENGTH != is.read(lenBuff)) {
            throw new InvalidParameterException("Unable to read value length.");
        }

        int len = ByteBuffer.wrap(lenBuff).getInt();
        byte[] valueArray = new byte[len];
        if (len != is.read(valueArray)) {
            throw new InvalidParameterException("Unable to read value.");
        }

        return new BigInteger(valueArray);
    }
}

希望这对您有所帮助。