从 PEM BASE64 编码的私钥文件获取 RSA 私钥

java cryptography certificate x509 pkcs#8

2022-09-01 07:04:32

我有一个私钥文件（PEM BASE64编码）。我想在其他地方使用它来解密其他一些数据。下面是 java 类代码段，用于读取私钥文件并解码其中的 BASE64 编码数据。

import java.io.*;
import java.nio.ByteBuffer;
import java.security.*;
import java.security.spec.PKCS8EncodedKeySpec;
import com.ibm.crypto.fips.provider.RSAPrivateKey;
import com.ibm.misc.BASE64Decoder;

public class GetPrivateKey {
    public static RSAPrivateKey get() throws Exception {
        File privateKeyFile = new File("privatekey.key");
        byte[] encodedKey = new byte[(int) privateKeyFile.length()];
        new FileInputStream(privateKeyFile).read(encodedKey);
        ByteBuffer keyBytes = new BASE64Decoder().decodeBufferToByteBuffer(encodedKey.toString());
        PKCS8EncodedKeySpec privateKeySpec = new PKCS8EncodedKeySpec(keyBytes.array());
        KeyFactory kf = KeyFactory.getInstance("RSA", "IBMJCEFIPS");
        RSAPrivateKey pk = (RSAPrivateKey) kf.generatePrivate(privateKeySpec);
        return pk;
    }

    public static void main(String[] args) throws Exception {
        PrivateKey privKey = FormatMePlease.get();
        System.out.println(privKey.toString());
    }

}

我收到以下错误

Exception in thread "main" java.security.spec.InvalidKeySpecException: Inappropriate key specification: DerInputStream.getLength(): lengthTag=127, too big.
at com.ibm.crypto.fips.provider.RSAKeyFactory.b(Unknown Source)
at com.ibm.crypto.fips.provider.RSAKeyFactory.engineGeneratePrivate(Unknown Source)
at java.security.KeyFactory.generatePrivate(Unknown Source)
at GetPrivateKey.get(GetPrivateKey.java:24)
at GetPrivateKey.main(GetPrivateKey.java:29)

文件的内容privatekey.key

类似的问题也在这里发布，但这些对我没有帮助。几乎所有人都建议使用 Bouncycastle 提供程序，我无法使用，因为我仅限于使用符合 FIPS 的提供程序，我不确定 BC 提供程序是否符合 FIPS 标准。

帮助解决这个问题将不胜感激。提前致谢。

答案 1

这是私钥的 PKCS#1 格式。请尝试此代码。它不使用Bouncy Castle或其他第三方加密提供商。只是java.security和sun.security for DER sequece parsing。此外，它还支持解析PKCS#8格式的私钥（具有标头“-----BEGIN私钥-----）的PEM文件）。

import sun.security.util.DerInputStream;
import sun.security.util.DerValue;

import java.io.File;
import java.io.IOException;
import java.math.BigInteger;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.security.GeneralSecurityException;
import java.security.KeyFactory;
import java.security.PrivateKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.RSAPrivateCrtKeySpec;
import java.util.Base64;

public static PrivateKey pemFileLoadPrivateKeyPkcs1OrPkcs8Encoded(File pemFileName) throws GeneralSecurityException, IOException {
        // PKCS#8 format
        final String PEM_PRIVATE_START = "-----BEGIN PRIVATE KEY-----";
        final String PEM_PRIVATE_END = "-----END PRIVATE KEY-----";

        // PKCS#1 format
        final String PEM_RSA_PRIVATE_START = "-----BEGIN RSA PRIVATE KEY-----";
        final String PEM_RSA_PRIVATE_END = "-----END RSA PRIVATE KEY-----";

        Path path = Paths.get(pemFileName.getAbsolutePath());

        String privateKeyPem = new String(Files.readAllBytes(path));

        if (privateKeyPem.indexOf(PEM_PRIVATE_START) != -1) { // PKCS#8 format
            privateKeyPem = privateKeyPem.replace(PEM_PRIVATE_START, "").replace(PEM_PRIVATE_END, "");
            privateKeyPem = privateKeyPem.replaceAll("\\s", "");

            byte[] pkcs8EncodedKey = Base64.getDecoder().decode(privateKeyPem);

            KeyFactory factory = KeyFactory.getInstance("RSA");
            return factory.generatePrivate(new PKCS8EncodedKeySpec(pkcs8EncodedKey));

        } else if (privateKeyPem.indexOf(PEM_RSA_PRIVATE_START) != -1) {  // PKCS#1 format

            privateKeyPem = privateKeyPem.replace(PEM_RSA_PRIVATE_START, "").replace(PEM_RSA_PRIVATE_END, "");
            privateKeyPem = privateKeyPem.replaceAll("\\s", "");

            DerInputStream derReader = new DerInputStream(Base64.getDecoder().decode(privateKeyPem));

            DerValue[] seq = derReader.getSequence(0);

            if (seq.length < 9) {
                throw new GeneralSecurityException("Could not parse a PKCS1 private key.");
            }

            // skip version seq[0];
            BigInteger modulus = seq[1].getBigInteger();
            BigInteger publicExp = seq[2].getBigInteger();
            BigInteger privateExp = seq[3].getBigInteger();
            BigInteger prime1 = seq[4].getBigInteger();
            BigInteger prime2 = seq[5].getBigInteger();
            BigInteger exp1 = seq[6].getBigInteger();
            BigInteger exp2 = seq[7].getBigInteger();
            BigInteger crtCoef = seq[8].getBigInteger();

            RSAPrivateCrtKeySpec keySpec = new RSAPrivateCrtKeySpec(modulus, publicExp, privateExp, prime1, prime2, exp1, exp2, crtCoef);

            KeyFactory factory = KeyFactory.getInstance("RSA");

            return factory.generatePrivate(keySpec);
        }

        throw new GeneralSecurityException("Not supported format of a private key");
    }

答案 2

您刚刚发布了该私钥，因此现在全世界都知道它是什么。希望这只是为了测试。

编辑：其他人已经注意到已发布密钥的openssl文本标题-----BEGIN RSA私钥-----,表示它是PKCS#1。但是，所讨论的密钥的实际 Base64 内容是 PKCS#8。显然，由于某种未知原因，OP将PKCS#1密钥的标题和预告片复制并粘贴到PKCS#8密钥上。我在下面提供的示例代码适用于 PKCS#8 私钥。

下面是一些将从该数据创建私钥的代码。您必须将 Base64 解码替换为 IBM Base64 解码器。

public class RSAToy {

    private static final String BEGIN_RSA_PRIVATE_KEY = "-----BEGIN RSA PRIVATE KEY-----\n"
            + "MIIEuwIBADAN ...skipped the rest\n"
         // + ...   
         // + ... skipped the rest
         // + ...   
            + "-----END RSA PRIVATE KEY-----";

    public static void main(String[] args) throws Exception {

        // Remove the first and last lines

        String privKeyPEM = BEGIN_RSA_PRIVATE_KEY.replace("-----BEGIN RSA PRIVATE KEY-----\n", "");
        privKeyPEM = privKeyPEM.replace("-----END RSA PRIVATE KEY-----", "");
        System.out.println(privKeyPEM);

        // Base64 decode the data

        byte [] encoded = Base64.decode(privKeyPEM);

        // PKCS8 decode the encoded RSA private key

        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(encoded);
        KeyFactory kf = KeyFactory.getInstance("RSA");
        PrivateKey privKey = kf.generatePrivate(keySpec);

        // Display the results

        System.out.println(privKey);
    }
}