如何将字符串从 PEM 转换为 DER 格式

java cryptography jce

2022-09-04 02:55:45

以以下格式发送字符串：

如何从这个字符串构造公钥对象？已尝试以下删除页眉和页脚，base64解码缓冲区

public static PublicKey getFromString(String keystr) throws Exception
  {
  //String S1= asciiToHex(keystr);
   byte[] keyBytes = new sun.misc.BASE64Decoder().decodeBuffer(keystr);
   X509EncodedKeySpec spec =
       new X509EncodedKeySpec(keyBytes);
     KeyFactory kf = KeyFactory.getInstance("RSA");
     return kf.generatePublic(spec);

  }

这会作为无效的密钥格式失败，或者会出现以下错误

java.security.spec.InvalidKeySpecException: java.security.InvalidKeyException: IOException: algid parse error, not a sequence
 at sun.security.rsa.RSAKeyFactory.engineGeneratePublic(RSAKeyFactory.java:188)
 at java.security.KeyFactory.generatePublic(KeyFactory.java:304)
 at PublicKeyReader.getFromString(PublicKeyReader.java:30)
 at Tst.main(Tst.java:36)

密钥正在通过 openSSL 的 API 生成PEM_write_bio_RSAPublicKey(bio, rsa);

答案 1

通过调用仅密钥模量和公共指数被编码到输出PEM数据中。但是，X509编码的密钥规范应采用以下ASN.1密钥格式：PEM_write_bio_RSAPublicKey

 SubjectPublicKeyInfo ::= SEQUENCE {
   algorithm AlgorithmIdentifier,
   subjectPublicKey BIT STRING }

您应该使用使用 SubjectPublicKeyInfo 结构对公钥进行编码的函数，该结构符合预期PEM_write_bio_PUBKEYX509EncodedKeySpec

解码密钥的另一种可能的解决方案。不幸的是，我不认为只能使用标准的JDK API来完成，但它可以通过Bouncycastle库来完成。

import org.bouncycastle.asn1.*;
import org.bouncycastle.asn1.x509.RSAPublicKeyStructure;

public static PublicKey getFromString(String keystr) throws Exception
{
  //String S1= asciiToHex(keystr);
   byte[] keyBytes = new sun.misc.BASE64Decoder().decodeBuffer(keystr);
   ASN1InputStream in = new ASN1InputStream(keyBytes);
   DERObject obj = in.readObject();
   RSAPublicKeyStructure pStruct = RSAPublicKeyStructure.getInstance(obj);
   RSAPublicKeySpec spec = new RSAPublicKeySpec(pStrcut.getModulus(), pStruct.getPublicExponent());
   KeyFactory kf = KeyFactory.getInstance("RSA");
   return kf.generatePublic(spec);
}

答案 2

BouncyCastle的PEMReader将为您完成此操作：

String pemKey = "-----BEGIN RSA PUBLIC KEY-----\n"
            + "MIGHAoGBANAahj75ZIz9nXqW2H83nGcUao4wNyYZ9Z1kiNTUYQl7ob/RBmDzs5rY\n"
            + "mUahXAg0qyS7+a55eU/csShf5ATGzAXv+DDPcz8HrSTcHMEFpuyYooX6PrIZ07Ma\n"
            + "XtsJ2J4mhlySI5uOZVRDoaFY53MPQx5gud2quDz759IN/0gnDEEVAgED\n"
            + "-----END RSA PUBLIC KEY-----\n";
PEMReader pemReader = new PEMReader(new StringReader(pemKey));
RSAPublicKey rsaPubKey = (RSAPublicKey) pemReader.readObject();
System.out.println("Public key: "+rsaPubKey);

（请注意，您可能需要之前的某个地方。Security.addProvider(new BouncyCastleProvider());