[英]Reading a PKCS#1 or SPKI public key in Java without libraries
我需要使用公鑰來驗證Java中的一些數據,但我似乎無法以不使用第三方插件的Java可以使用的方式格式化密鑰。
我正在使用Node.js的crypto
庫生成密鑰,它為我提供了PKCS#1
或SPKI
以及.pem或.der文件格式的選項。
我聽說Java不支持開箱即用的PKCS#1
,並且StackOverflow上幾乎所有其他答案都建議使用BouncyCastle或類似的,但在我的情況下,我正在編寫SDK,而且根本無力承擔使用庫只是為了讀取這個公鑰。
所以我現在正在讀取.der格式的密鑰,因為它節省了必須剝離PEM頭並從base-64解碼密鑰。 當我運行它時,我收到錯誤:
java.security.spec.InvalidKeySpecException: java.lang.RuntimeException: error:0c0000be:ASN.1 encoding routines:OPENSSL_internal:WRONG_TAG
這就是我所擁有的(抱歉,它在Kotlin中,而不是像標題所暗示的Java)
// Here's a key for convenience
val key = Base64.getDecoder().decode("MFUCTgF/uLsPBS13Gy7C3dPpiDF6SYCLUyyl6CFqPtZT1h5bwKR9EDFLQjG/kMiwkRMcmEeaLKe5qdj9W/FfFitwRAm/8F53pQw2UETKQI2b2wIDAQAB");
val keySpec = X509EncodedKeySpec(key)
val keyFactory = KeyFactory.getInstance("RSA")
val publicKey = keyFactory.generatePublic(keySpec) // error thrown here
val cipher = Cipher.getInstance("RSA/NONE/PKCS1Padding")
cipher.init(Cipher.DECRYPT_MODE, publicKey)
我最好的想法是在Node.js端安裝一個庫,這個問題較少,支持將密鑰導出為PKCS#8,但我想我先檢查一下,看看我是否遺漏了什么。
以下代碼將PKCS#1編碼的公鑰轉換為SubjectPublicKeyInfo編碼的公鑰,該公鑰是RSA KeyFactory
使用X509EncodedKeySpec
接受的公鑰編碼 - 因為在X.509規范中定義了SubjectPublicKeyInfo。
基本上它是一種低級DER編碼方案
0x03
,以及未使用位數的編碼,一個值為0x00
的字節); 0x30
)。 沒有使用庫。 實際上,對於createSubjectPublicKeyInfoEncoding
,甚至不需要import語句。
import java.security.KeyFactory;
import java.security.NoSuchAlgorithmException;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.X509EncodedKeySpec;
import java.util.Base64;
public class PKCS1ToSubjectPublicKeyInfo {
private static final int SEQUENCE_TAG = 0x30;
private static final int BIT_STRING_TAG = 0x03;
private static final byte[] NO_UNUSED_BITS = new byte[] { 0x00 };
private static final byte[] RSA_ALGORITHM_IDENTIFIER_SEQUENCE =
{(byte) 0x30, (byte) 0x0d,
(byte) 0x06, (byte) 0x09, (byte) 0x2a, (byte) 0x86, (byte) 0x48, (byte) 0x86, (byte) 0xf7, (byte) 0x0d, (byte) 0x01, (byte) 0x01, (byte) 0x01,
(byte) 0x05, (byte) 0x00};
public static RSAPublicKey decodePKCS1PublicKey(byte[] pkcs1PublicKeyEncoding)
throws NoSuchAlgorithmException, InvalidKeySpecException
{
byte[] subjectPublicKeyInfo2 = createSubjectPublicKeyInfoEncoding(pkcs1PublicKeyEncoding);
KeyFactory rsaKeyFactory = KeyFactory.getInstance("RSA");
RSAPublicKey generatePublic = (RSAPublicKey) rsaKeyFactory.generatePublic(new X509EncodedKeySpec(subjectPublicKeyInfo2));
return generatePublic;
}
public static byte[] createSubjectPublicKeyInfoEncoding(byte[] pkcs1PublicKeyEncoding)
{
byte[] subjectPublicKeyBitString = createDEREncoding(BIT_STRING_TAG, concat(NO_UNUSED_BITS, pkcs1PublicKeyEncoding));
byte[] subjectPublicKeyInfoValue = concat(RSA_ALGORITHM_IDENTIFIER_SEQUENCE, subjectPublicKeyBitString);
byte[] subjectPublicKeyInfoSequence = createDEREncoding(SEQUENCE_TAG, subjectPublicKeyInfoValue);
return subjectPublicKeyInfoSequence;
}
private static byte[] concat(byte[] ... bas)
{
int len = 0;
for (int i = 0; i < bas.length; i++)
{
len += bas[i].length;
}
byte[] buf = new byte[len];
int off = 0;
for (int i = 0; i < bas.length; i++)
{
System.arraycopy(bas[i], 0, buf, off, bas[i].length);
off += bas[i].length;
}
return buf;
}
private static byte[] createDEREncoding(int tag, byte[] value)
{
if (tag < 0 || tag >= 0xFF)
{
throw new IllegalArgumentException("Currently only single byte tags supported");
}
byte[] lengthEncoding = createDERLengthEncoding(value.length);
int size = 1 + lengthEncoding.length + value.length;
byte[] derEncodingBuf = new byte[size];
int off = 0;
derEncodingBuf[off++] = (byte) tag;
System.arraycopy(lengthEncoding, 0, derEncodingBuf, off, lengthEncoding.length);
off += lengthEncoding.length;
System.arraycopy(value, 0, derEncodingBuf, off, value.length);
return derEncodingBuf;
}
private static byte[] createDERLengthEncoding(int size)
{
if (size <= 0x7F)
{
// single byte length encoding
return new byte[] { (byte) size };
}
else if (size <= 0xFF)
{
// double byte length encoding
return new byte[] { (byte) 0x81, (byte) size };
}
else if (size <= 0xFFFF)
{
// triple byte length encoding
return new byte[] { (byte) 0x82, (byte) (size >> Byte.SIZE), (byte) size };
}
throw new IllegalArgumentException("size too large, only up to 64KiB length encoding supported: " + size);
}
public static void main(String[] args) throws Exception
{
// some weird 617 bit key, which is way too small and not a multiple of 8
byte[] pkcs1PublicKeyEncoding = Base64.getDecoder().decode("MFUCTgF/uLsPBS13Gy7C3dPpiDF6SYCLUyyl6CFqPtZT1h5bwKR9EDFLQjG/kMiwkRMcmEeaLKe5qdj9W/FfFitwRAm/8F53pQw2UETKQI2b2wIDAQAB");
RSAPublicKey generatePublic = decodePKCS1PublicKey(pkcs1PublicKeyEncoding);
System.out.println(generatePublic);
}
}
筆記:
NoSuchAlgorithmException
並將其放入RuntimeException
; createDERLengthEncoding
應該不接受負大小。 createDERLengthEncoding
- 我認為它有效,但最好是安全而不是抱歉。
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