如何在Java中使用RSAPrivateKeySpec类从字符串创建RSA私钥?

Question

我有以下信息，想在RSA(Java)中生成公钥和私钥。

String pubKey = "MFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBAJXFRUWMDJZ+moC/VbcAXoY5dDxOruwI2B+B+YZRHSRRTKPyd9v0HTqdLeVgufLu/cSxlZAKtZDp9mfgyNdbY9ECAwEAAQ==";
String privKey = "MIIBVAIBADANBgkqhkiG9w0BAQEFAASCAT4wggE6AgEAAkEAlcVFRYwMln6agL9VtwBehjl0PE6u7AjYH4H5hlEdJFFMo/J32/QdOp0t5WC58u79xLGVkAq1kOn2Z+DI11tj0QIDAQABAkBC1Bp71OkNAgL47edWWADVja9y9X0R70RYkst/hpQlTrjN4QxzN4k4gCqqdFkno2LfacRO7igMQuVEmYujfkbNAiEA/lU1CyW9J65FXSObsBLxqlNpFw79B2EKUkT6o7b2Ez8CIQCWwJlIyDaoXt7CrvTrPDpok7U93ZKmDPiRjjXDPsGU7wIhAJ6pITIXFO2QNg1ojVNGPiR3bHPKEedsjjfMeF9xYAmZAiAQnfpHg4pC1PJJE2/73g+yJ1X7E8ludE+R+9MBSpGcEQIgBWaVSyTx4e+gSulT93vnMpVsYmiwe53e5t4Uxs+cgSE=";
String nModulusPublic = "AJXFRUWMDJZ-moC_VbcAXoY5dDxOruwI2B-B-YZRHSRRTKPyd9v0HTqdLeVgufLu_cSxlZAKtZDp9mfgyNdbY9E=";
String eExponentPublic = "AQAB";
String nModulusPrivate = "AJXFRUWMDJZ-moC_VbcAXoY5dDxOruwI2B-B-YZRHSRRTKPyd9v0HTqdLeVgufLu_cSxlZAKtZDp9mfgyNdbY9E=";
String eExponentPrivate = "QtQae9TpDQIC-O3nVlgA1Y2vcvV9Ee9EWJLLf4aUJU64zeEMczeJOIAqqnRZJ6Ni32nETu4oDELlRJmLo35GzQ==";

这些是主要的加密和解密功能：

static String Decrypt(String encodedString,PrivateKey privKey) {
try {
Cipher cipher = Cipher.getInstance(cipherInstancename);
cipher.init(Cipher.DECRYPT_MODE, privKey);
byte[] decrypted = cipher.doFinal(Base64.getDecoder().decode(encodedString));
return new String(decrypted, "UTF-8");
} catch (Exception err) {
return err.fillInStackTrace().toString();
}
}
static String Encrypt(String encodedString,PublicKey pubKey) {
try {
Cipher cipher = Cipher.getInstance(cipherInstancename);
cipher.init(Cipher.ENCRYPT_MODE, pubKey);
byte[] plainBytes = new String(encodedString).getBytes("UTF-8");
byte[] cipherData = cipher.doFinal(plainBytes);
String encryptedString = Base64.getEncoder().encodeToString(cipherData);
return encryptedString;
} catch (Exception err) {
return err.fillInStackTrace().toString();
}
}

如果我使用以下函数创建私钥和公钥，一切正常：

static PrivateKey firstPrivateKey(String privateKeyStr) throws Exception {
byte[] keyBytes = Base64.getDecoder().decode(privateKeyStr.getBytes(StandardCharsets.UTF_8));
PKCS8EncodedKeySpec specPrivate = new PKCS8EncodedKeySpec(keyBytes);
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
PrivateKey fileGeneratedPrivateKey = keyFactory.generatePrivate(specPrivate);
RSAPrivateKey rsaPrv  = (RSAPrivateKey)(fileGeneratedPrivateKey);
return  rsaPrv;
}
static PublicKey firstPublicKey(String publicKeyStr) throws Exception {
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
byte[] keyBytes = Base64.getDecoder().decode(publicKeyStr.getBytes(StandardCharsets.UTF_8));
X509EncodedKeySpec specPublic = new X509EncodedKeySpec(keyBytes);
PublicKey fileGeneratedPublicKey = keyFactory.generatePublic(specPublic);
RSAPublicKey rsaPub  = (RSAPublicKey)(fileGeneratedPublicKey);
return  rsaPub;
}

但是我想使用以下功能以这种方式创建它们，但解密不起作用：

static PublicKey secondPublicKey(String publicKString,String publicExponentStr) throws Exception {
byte[] modulusBytes = Base64.getDecoder().decode(publicKString);
byte[] exponentBytes = Base64.getDecoder().decode(publicExponentStr);
BigInteger modulus = new BigInteger(1, modulusBytes);
BigInteger exponent = new BigInteger(1, exponentBytes);
RSAPublicKeySpec rsaPubKey = new RSAPublicKeySpec(modulus, exponent);
KeyFactory fact = KeyFactory.getInstance("RSA");
PublicKey pubKey = fact.generatePublic(rsaPubKey);
return pubKey;
}
static PrivateKey secondPrivateKey(String privateKString,String privateExponentStr) throws Exception {
byte[] modulusBytes = Base64.getDecoder().decode(privateKString);
byte[] exponentBytes = Base64.getDecoder().decode(privateExponentStr);
BigInteger modulus = new BigInteger(1, modulusBytes);
BigInteger exponent = new BigInteger(1, exponentBytes);
RSAPrivateKeySpec privSpec = new RSAPrivateKeySpec(modulus,exponent);
KeyFactory fact = KeyFactory.getInstance("RSA");
PrivateKey privKey = fact.generatePrivate(privSpec);
return privKey;
}

使用firstPrivateKey和firstPublicKey密钥生成器，工作得很好：

String a = Encrypt("test",firstPrivateKey(pubKey));
String b = Decrypt(a, firstPublicKey(privKey));
System.out.println(b);

使用第二个函数并且不起作用：

String a = Encrypt("test",secondPublicKey(pubKey,eExponentPublic));
String b = Decrypt(a, secondPrivateKey(privKey,eExponentPrivate));
System.out.println(b);

secondPublicKey 和 secondPrivateKey 函数有什么问题？

更新：

我从这段代码生成所有密钥和模数，看来我的解码不行：

KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
// RSAKeyGenParameterSpec spec = new RSAKeyGenParameterSpec(1024, RSAKeyGenParameterSpec.F4);
kpg.initialize( 512 );
KeyPair kp = kpg.generateKeyPair();
String publicKeyStr = Base64.getEncoder().encodeToString(kp.getPublic().getEncoded());
String privateKeyStr = Base64.getEncoder().encodeToString(kp.getPrivate().getEncoded());
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
byte[] keyBytes = Base64.getDecoder().decode(publicKeyStr.getBytes(StandardCharsets.UTF_8));
X509EncodedKeySpec specPublic = new X509EncodedKeySpec(keyBytes);
PublicKey fileGeneratedPublicKey = keyFactory.generatePublic(specPublic);
RSAPublicKey rsaPub  = (RSAPublicKey)(fileGeneratedPublicKey);
keyBytes = Base64.getDecoder().decode(privateKeyStr.getBytes(StandardCharsets.UTF_8));
PKCS8EncodedKeySpec specPrivate = new PKCS8EncodedKeySpec(keyBytes);
PrivateKey fileGeneratedPrivateKey = keyFactory.generatePrivate(specPrivate);
RSAPrivateKey rsaPrv  = (RSAPrivateKey)(fileGeneratedPrivateKey);

BigInteger publicKeyModulus = rsaPub.getModulus();
BigInteger publicKeyExponent  = rsaPub.getPublicExponent();
BigInteger privateKeyModulus = rsaPrv.getModulus();
BigInteger privateKeyExponent  = rsaPrv.getPrivateExponent();

String nModulusPublic=Base64.getUrlEncoder().encodeToString(publicKeyModulus.toByteArray());
String eExponentPublic=Base64.getUrlEncoder().encodeToString(publicKeyExponent.toByteArray());
String nModulusPrivate=Base64.getUrlEncoder().encodeToString(privateKeyModulus.toByteArray());
String eExponentPrivate=Base64.getUrlEncoder().encodeToString(privateKeyExponent.toByteArray());
System.out.println(publicKeyStr);
System.out.println(privateKeyStr);
System.out.println( nModulusPublic);
System.out.println(eExponentPublic);
System.out.println( nModulusPrivate);
System.out.println(eExponentPrivate);

Answer 1

相关的公钥和私钥具有相同的模数。因此，nModulusPublic和nModulusPrivate之间的区别实际上没有必要(与公共指数和私人指数不同)。

secondPublicKey()和secondPrivateKey()期望模数(nModulusPublic或相同的nModulusPrivate)作为第一个参数。相反，传递整个密钥(pubKey或privKey)，这会导致错误。如果传递模量，则它可以工作。

顺便说一下，模数和指数是 Base64url 编码的，必须首先转换为标准的 Base64 编码(-->+和_->/)。或者，Base64url解码器可以在secondPublicKey()或secondPrivateKey()中使用(Base64.getUrlDecoder())。

由于两个公钥或私钥是相同的(只是格式不同)，因此任何公钥/私钥组合都可以进行加密/解密：

String pubKey = "MFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBAJXFRUWMDJZ+moC/VbcAXoY5dDxOruwI2B+B+YZRHSRRTKPyd9v0HTqdLeVgufLu/cSxlZAKtZDp9mfgyNdbY9ECAwEAAQ==";
String privKey = "MIIBVAIBADANBgkqhkiG9w0BAQEFAASCAT4wggE6AgEAAkEAlcVFRYwMln6agL9VtwBehjl0PE6u7AjYH4H5hlEdJFFMo/J32/QdOp0t5WC58u79xLGVkAq1kOn2Z+DI11tj0QIDAQABAkBC1Bp71OkNAgL47edWWADVja9y9X0R70RYkst/hpQlTrjN4QxzN4k4gCqqdFkno2LfacRO7igMQuVEmYujfkbNAiEA/lU1CyW9J65FXSObsBLxqlNpFw79B2EKUkT6o7b2Ez8CIQCWwJlIyDaoXt7CrvTrPDpok7U93ZKmDPiRjjXDPsGU7wIhAJ6pITIXFO2QNg1ojVNGPiR3bHPKEedsjjfMeF9xYAmZAiAQnfpHg4pC1PJJE2/73g+yJ1X7E8ludE+R+9MBSpGcEQIgBWaVSyTx4e+gSulT93vnMpVsYmiwe53e5t4Uxs+cgSE=";
String nModulusPublic = "AJXFRUWMDJZ-moC_VbcAXoY5dDxOruwI2B-B-YZRHSRRTKPyd9v0HTqdLeVgufLu_cSxlZAKtZDp9mfgyNdbY9E=".replace("-", "+").replace("_","/");
String eExponentPublic = "AQAB".replace("-", "+").replace("_","/");
String nModulusPrivate = "AJXFRUWMDJZ-moC_VbcAXoY5dDxOruwI2B-B-YZRHSRRTKPyd9v0HTqdLeVgufLu_cSxlZAKtZDp9mfgyNdbY9E=".replace("-", "+").replace("_","/");
String eExponentPrivate = "QtQae9TpDQIC-O3nVlgA1Y2vcvV9Ee9EWJLLf4aUJU64zeEMczeJOIAqqnRZJ6Ni32nETu4oDELlRJmLo35GzQ==".replace("-", "+").replace("_","/");    
String a, b;
// first/first
a = Encrypt("test", firstPublicKey(pubKey));
b = Decrypt(a, firstPrivateKey(privKey));
System.out.println(b);
// second/second
a = Encrypt("test", secondPublicKey(nModulusPublic, eExponentPublic));
b = Decrypt(a, secondPrivateKey(nModulusPrivate, eExponentPrivate));
System.out.println(b);
// first/second
a = Encrypt("test", firstPublicKey(pubKey));
b = Decrypt(a, secondPrivateKey(nModulusPrivate, eExponentPrivate));
System.out.println(b);
// second/first
a = Encrypt("test", secondPublicKey(nModulusPublic, eExponentPublic));
b = Decrypt(a, firstPrivateKey(privKey));
System.out.println(b);

请注意，发布的代码中有一个拼写错误：Encrypt与firstPrivateKey()结合使用，Decrypt与firstPublicKey()结合使用。