問題描述

以以下格式發送字符串:

Have a String being sent from in the below format:

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

如何從這個字符串構造一個 PublicKey 對象?已嘗試以下去掉頁眉頁腳和base64解碼緩沖區

How do i construct a PublicKey Object from this string ? Have tried the below Remove the header and footer and base64 decode the buffer

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);

  }

這會失敗，要么是無效的密鑰格式，要么會出現以下錯誤

This fails either as an invalid key format or will get below error

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)

正在通過openSSL的API生成密鑰PEM_write_bio_RSAPublicKey(bio, rsa);

The Key is being generated thro the API of openSSL PEM_write_bio_RSAPublicKey(bio, rsa);

推薦答案

通過調用 PEM_write_bio_RSAPublicKey，只有密鑰模數和公共指數被編碼到輸出 PEM 數據中.但是 X509EncodedKeySpec 應該是這種 ASN.1 密鑰格式:

by calling PEM_write_bio_RSAPublicKey only the key modulus and public exponent are encoded into the output PEM data. However the X509EncodedKeySpec is expected this ASN.1 key format:

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

您應該使用 PEM_write_bio_PUBKEY 函數，該函數使用 SubjectPublicKeyInfo 結構對公鑰進行編碼，正如 X509EncodedKeySpec

You should use the PEM_write_bio_PUBKEY function which encodes the public key using the SubjectPublicKeyInfo structure which as expected by X509EncodedKeySpec

解碼密鑰的另一種可能的解決方案.不幸的是，我認為不可能只使用標準 JDK API，但可以使用 Bouncycastle圖書館

An other possible solution to decode the key. Unfortunately I don't think it is possible to do only with the standard JDK API but it can be done with the Bouncycastle library

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);
}

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