我们如何将字符串从PEM转换为DER格式

Question

从以下格式发送字符串:

-----BEGIN RSA PUBLIC KEY-----
MIGHAoGBANAahj75ZIz9nXqW2H83nGcUao4wNyYZ9Z1kiNTUYQl7ob/RBmDzs5rY
mUahXAg0qyS7+a55eU/csShf5ATGzAXv+DDPcz8HrSTcHMEFpuyYooX6PrIZ07Ma
XtsJ2J4mhlySI5uOZVRDoaFY53MPQx5gud2quDz759IN/0gnDEEVAgED
-----END RSA PUBLIC KEY-----

如何从此字符串构造PublicKey对象？尝试了以下删除页眉和页脚和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);

  }

这可能会作为无效的密钥格式失败,也会失败

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)

密钥是通过openSSL的API生成的 PEM_write_bio_RSAPublicKey(bio, rsa);

Answer 1

通过PEM_write_bio_RSAPublicKey仅调用密钥模数和公共指数被编码到输出PEM数据中.但是,这X509EncodedKeySpec是ASN.1密钥格式的预期:

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

您应该使用PEM_write_bio_PUBKEYSubjectPublicKeyInfo结构对公钥进行编码的函数,该结构符合预期X509EncodedKeySpec

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JDK API,但可以使用Bouncycastle库完成

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);
}

Answer 2

BouncyCastle的PEMReader将为您完成此任务:

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Security.addProvider(new BouncyCastleProvider());之前可能需要某处.)