Rebuilding RSA private key from modulus and exponential failed
I’m trying to reconstruct RSA key pairs from modulus and private/public exponents. The conversion is correct for the public key, but cannot be converted to the private key when comparing the encoded private key.
When encrypted with this reconstructed private/public key pair, it works in
Java (!), but when using reconstructed key pair in PHP, decryption partially fails (encryption works), so it seems to me that the reconstructed private key is different from the “original” private key.
REFERENCE ONLY: Everything works fine in PHP with “raw” key pairs.
So my question is: how do I retrieve the “raw” private key from the (BigInteger) modulus and private index?
Edits: See my final edits at the end
My sample code shows the equality of the public key to the reconstructed key and the difference between the private key:
Rebuilding of a RSA PrivateKey from modulus & exponent
privateKey equals rebuild: false
publicKey equals rebuild: true
Code:
import java.math.BigInteger;
import java.security.*;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.RSAPrivateKeySpec;
import java.security.spec.RSAPublicKeySpec;
import java.util.Arrays;
public class RebuildRSAPrivateKey {
public static void main(String[] args) throws NoSuchAlgorithmException, InvalidKeySpecException {
System.out.println("Rebuilding of a RSA PrivateKey from modulus & exponent");
rsa key generation
KeyPairGenerator kpGen = KeyPairGenerator.getInstance("RSA");
kpGen.initialize(2048, new SecureRandom());
kpGen.initialize(2048, new SecureRandom());
KeyPair keyPair = kpGen.generateKeyPair();
private key
PrivateKey privateKey = keyPair.getPrivate();
get modulus & exponent
RSAPrivateKey rsaPrivateKey = (RSAPrivateKey) privateKey;
BigInteger modulus = rsaPrivateKey.getModulus();
BigInteger privateExponent = rsaPrivateKey.getPrivateExponent();
rebuild the private key
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
RSAPrivateKeySpec rsaPrivateKeySpec = new RSAPrivateKeySpec(modulus, privateExponent);
PrivateKey privateKeyRebuild = keyFactory.generatePrivate(rsaPrivateKeySpec);
System.out.println("privateKey equals rebuild: " + Arrays.equals(privateKey.getEncoded(), privateKeyRebuild.getEncoded()));
public key
PublicKey publicKey = keyPair.getPublic();
get modulus & exponent
RSAPublicKey rsaPublicKey = (RSAPublicKey) publicKey;
BigInteger modulusPub = rsaPublicKey.getModulus();
BigInteger publicExponent = rsaPublicKey.getPublicExponent();
rebuild the public key
KeyFactory keyFactoryPub = KeyFactory.getInstance("RSA");
RSAPublicKeySpec rsaPublicKeySpec = new RSAPublicKeySpec(modulusPub, publicExponent);
PublicKey publicKeyRebuild = keyFactory.generatePublic(rsaPublicKeySpec);
System.out.println("publicKey equals rebuild: " + Arrays.equals(publicKey.getEncoded(), publicKeyRebuild.getEncoded()));
}
}
EDIT: The following procedure will show that an RSA private/public key pair derived from the encoded key can be recovered and
Encryption and decryption are valid in Java and PHP. Key is insecure with RSA 512-bit keys and Base64 decoding.
Then derive the same key from the modulus and private/public exponents, and encryption/decryption works in Java but not in PHP.
That’s why I want to get the “raw” RSA key from modulus and exponent, thanks for your eager help.
Results of Java programs:
Rebuilding of a RSA PrivateKey from modulus & exponent v4
privateKey Original Base64: MIIBVgIBADANBgkqhkiG9w0BAQEFAASCAUAwggE8AgEAAkEA2wFgcni89ijJ/uijQkzCGF4JiUB1+mEJ48u4Lk0vxB7ym3/FCvOEnN2H7FLUzsGvXRhFriLBiSJlg2tOhV5eiwIDAQABAkEAkDpf4gNRrms+W/ mpSshyKsoDTbh9+d5ePP601QlQI79lrsjdy2GLgk4RV1XmwYinM9Sk8G+ssyXTYHdby6A2wQIhAPcRtl6tub6PFiIE1jcuIkib/ HzAdRYHZx3ZdzRTYDetAiEA4uv43xpGl5N8yG27Kv0DkRoOlr4Ch6oM24hLVw7ClhcCIFgdRAo+MQlqJH2bdf6WAHoez4x6YwepOjhmD2Jk/eK9AiEAtHgI6J5EEB56+gfS+CBa6tZ3Tcl1x6ElMp8Vk/ ooJScCIQDUa3LUkcc58yjJYq8ZNQC/86+HIzd5MldTwg5buR1lpw==
privateKey Rebuild Base64: MIIBVgIBADANBgkqhkiG9w0BAQEFAASCAUAwggE8AgEAAkEA2wFgcni89ijJ/uijQkzCGF4JiUB1+mEJ48u4Lk0vxB7ym3/FCvOEnN2H7FLUzsGvXRhFriLBiSJlg2tOhV5eiwIDAQABAkEAkDpf4gNRrms+W/ mpSshyKsoDTbh9+d5ePP601QlQI79lrsjdy2GLgk4RV1XmwYinM9Sk8G+ssyXTYHdby6A2wQIhAPcRtl6tub6PFiIE1jcuIkib/ HzAdRYHZx3ZdzRTYDetAiEA4uv43xpGl5N8yG27Kv0DkRoOlr4Ch6oM24hLVw7ClhcCIFgdRAo+MQlqJH2bdf6WAHoez4x6YwepOjhmD2Jk/eK9AiEAtHgI6J5EEB56+gfS+CBa6tZ3Tcl1x6ElMp8Vk/ ooJScCIQDUa3LUkcc58yjJYq8ZNQC/86+HIzd5MldTwg5buR1lpw==
publicKey Base64: MFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBANsBYHJ4vPYoyf7oo0JMwhheCYlAdfphCePLuC5NL8Qe8pt/xQrzhJzdh+xS1M7Br10YRa4iwYkiZYNrToVeXosCAwEAAQ==
generate private & public key via modulus and private/public exponent
privateKey Modulus Base64: MIGzAgEAMA0GCSqGSIb3DQEBAQUABIGeMIGbAgEAAkEA2wFgcni89ijJ/uijQkzCGF4JiUB1+mEJ48u4Lk0vxB7ym3/FCvOEnN2H7FLUzsGvXRhFriLBiSJlg2tOhV5eiwIBAAJBAJA6X+ IDUa5rPlv5qUrIcirKA024ffneXjz+tNUJUCO/Za7I3cthi4JOEVdV5sGIpzPUpPBvrLMl02B3W8ugNsECAQACAQACAQACAQACAQA=
publicKey Modulus Base64: MFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBANsBYHJ4vPYoyf7oo0JMwhheCYlAdfphCePLuC5NL8Qe8pt/xQrzhJzdh+xS1M7Br10YRa4iwYkiZYNrToVeXosCAwEAAQ==
en-/decryption with original keys
ciphertext Original : fvFPRZ5B2GMgv9aXQjyQsxnRHK2wotfXlLV+zGea1E3nsZC6RMn+LQMOe9yvZ8IcaG2F/8wWv2NkNmBX4wuxaw==
decryptedtext Original: this is the message to encrypt
en-/decryption with keys from modulus & exponent
ciphertext Modulus : o0tB4xQIwQRFDSsWj1WgWHexXnJOp9jeBymFPJvy+xZBvfJay2yR0XZEy+0VwaedxdTf9CoyKVvgCbn2HCohSQ==
decryptedtext Modulus : this is the message to encrypt
Results of PHP program:
php version: 7.4.6 openssl version: OpenSSL 1.1.1g 21 Apr 2020
plaintext: this is the message to encrypt
rsa encryption with original keys
priBase64: MIIBVgIBADANBgkqhkiG9w0BAQEFAASCAUAwggE8AgEAAkEA2wFgcni89ijJ/uijQkzCGF4JiUB1+mEJ48u4Lk0vxB7ym3/FCvOEnN2H7FLUzsGvXRhFriLBiSJlg2tOhV5eiwIDAQABAkEAkDpf4gNRrms+W/ mpSshyKsoDTbh9+d5ePP601QlQI79lrsjdy2GLgk4RV1XmwYinM9Sk8G+ssyXTYHdby6A2wQIhAPcRtl6tub6PFiIE1jcuIkib/ HzAdRYHZx3ZdzRTYDetAiEA4uv43xpGl5N8yG27Kv0DkRoOlr4Ch6oM24hLVw7ClhcCIFgdRAo+MQlqJH2bdf6WAHoez4x6YwepOjhmD2Jk/eK9AiEAtHgI6J5EEB56+gfS+CBa6tZ3Tcl1x6ElMp8Vk/ ooJScCIQDUa3LUkcc58yjJYq8ZNQC/86+HIzd5MldTwg5buR1lpw==
pubBase64:MFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBANsBYHJ4vPYoyf7oo0JMwhheCYlAdfphCePLuC5NL8Qe8pt/xQrzhJzdh+xS1M7Br10YRa4iwYkiZYNrToVeXosCAwEAAQ==
ciphertext Base64:WmvVwqf2EHQc0yb6L4pVJ0/23pNW4QsBun3SNvYE8p/sEk+1GQSYxYpbY/mLbSGF2Lb1P5g5er+z7dWxHmodNA==
decryptedtext: this is the message to encrypt
rsa encryption with keys created via modulus & exponents
priBase64: MIGzAgEAMA0GCSqGSIb3DQEBAQUABIGeMIGbAgEAAkEA2wFgcni89ijJ/uijQkzCGF4JiUB1+mEJ48u4Lk0vxB7ym3/FCvOEnN2H7FLUzsGvXRhFriLBiSJlg2tOhV5eiwIBAAJBAJA6X+ IDUa5rPlv5qUrIcirKA024ffneXjz+tNUJUCO/Za7I3cthi4JOEVdV5sGIpzPUpPBvrLMl02B3W8ugNsECAQACAQACAQACAQACAQA=
pubBase64:MFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBANsBYHJ4vPYoyf7oo0JMwhheCYlAdfphCePLuC5NL8Qe8pt/xQrzhJzdh+xS1M7Br10YRa4iwYkiZYNrToVeXosCAwEAAQ==
ciphertext Base64:kqn8aZpvfpPzr3u2NBX/XmnlFweEvOm+Qu4l2wiUSQCjA0hutQ10mbLaO55oCox7GixvMgb3VtoDBJ8hfW1zbQ==
Cannot Decrypt error:0407109F:rsa routines:RSA_padding_check_PKCS1_type_2:pkcs decoding error
decryptedtext:
decrypt error: error:0909006C:PEM routines:get_name:no start line
Source code:
import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import java.io.IOException;
import java.math.BigInteger;
import java.security.*;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.*;
import java.util.Base64;
public class RebuildRSAPrivateKey4 {
public static void main(String[] args) throws NoSuchAlgorithmException, InvalidKeySpecException, IllegalBlockSizeException, InvalidKeyException, BadPaddingException, NoSuchPaddingException, IOException {
System.out.println("Rebuilding of a RSA PrivateKey from modulus & exponent v4");
rsa key generation
KeyPairGenerator kpGen = KeyPairGenerator.getInstance("RSA");
kpGen.initialize(2048, new SecureRandom());
kpGen.initialize(512, new SecureRandom()); don't use 512 bit keys as they are insecure !!
KeyPair keyPair = kpGen.generateKeyPair();
privateKey Base64: MIIBVgIBADANBgkqhkiG9w0BAQEFAASCAUAwggE8AgEAAkEA2wFgcni89ijJ/uijQkzCGF4JiUB1+mEJ48u4Lk0vxB7ym3/FCvOEnN2H7FLUzsGvXRhFriLBiSJlg2tOhV5eiwIDAQABAkEAkDpf4gNRrms+W/ mpSshyKsoDTbh9+d5ePP601QlQI79lrsjdy2GLgk4RV1XmwYinM9Sk8G+ssyXTYHdby6A2wQIhAPcRtl6tub6PFiIE1jcuIkib/ HzAdRYHZx3ZdzRTYDetAiEA4uv43xpGl5N8yG27Kv0DkRoOlr4Ch6oM24hLVw7ClhcCIFgdRAo+MQlqJH2bdf6WAHoez4x6YwepOjhmD2Jk/eK9AiEAtHgI6J5EEB56+gfS+CBa6tZ3Tcl1x6ElMp8Vk/ ooJScCIQDUa3LUkcc58yjJYq8ZNQC/86+HIzd5MldTwg5buR1lpw==
publicKey Base64: MFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBANsBYHJ4vPYoyf7oo0JMwhheCYlAdfphCePLuC5NL8Qe8pt/xQrzhJzdh+xS1M7Br10YRa4iwYkiZYNrToVeXosCAwEAAQ==
String privateKeyBase64 = "MIIBVgIBADANBgkqhkiG9w0BAQEFAASCAUAwggE8AgEAAkEA2wFgcni89ijJ/uijQkzCGF4JiUB1+mEJ48u4Lk0vxB7ym3/FCvOEnN2H7FLUzsGvXRhFriLBiSJlg2tOhV5eiwIDAQABAkEAkDpf4gNRrms+W/ mpSshyKsoDTbh9+d5ePP601QlQI79lrsjdy2GLgk4RV1XmwYinM9Sk8G+ssyXTYHdby6A2wQIhAPcRtl6tub6PFiIE1jcuIkib/ HzAdRYHZx3ZdzRTYDetAiEA4uv43xpGl5N8yG27Kv0DkRoOlr4Ch6oM24hLVw7ClhcCIFgdRAo+MQlqJH2bdf6WAHoez4x6YwepOjhmD2Jk/eK9AiEAtHgI6J5EEB56+gfS+CBa6tZ3Tcl1x6ElMp8Vk/ ooJScCIQDUa3LUkcc58yjJYq8ZNQC/86+HIzd5MldTwg5buR1lpw==";
String publicKeyBase64 = "MFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBANsBYHJ4vPYoyf7oo0JMwhheCYlAdfphCePLuC5NL8Qe8pt/xQrzhJzdh+xS1M7Br10YRa4iwYkiZYNrToVeXosCAwEAAQ==";
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
PKCS8EncodedKeySpec privateKeySpec = new PKCS8EncodedKeySpec(Base64.getDecoder().decode(privateKeyBase64));
PrivateKey privateKey = keyFactory.generatePrivate(privateKeySpec);
X509EncodedKeySpec publicKeySpec = new X509EncodedKeySpec(Base64.getDecoder().decode(publicKeyBase64));
PublicKey publicKey = keyFactory.generatePublic(publicKeySpec);
System.out.println("privateKey Original Base64: " + privateKeyBase64);
System.out.println("privateKey Rebuild Base64: " + Base64.getEncoder().encodeToString(privateKey.getEncoded()));
System.out.println("publicKey Base64: " + publicKeyBase64);
get modulus & private exponent via RSAPrivateKey
RSAPrivateKey rsaPrivateKey = (RSAPrivateKey) privateKey;
BigInteger modulus = rsaPrivateKey.getModulus();
BigInteger privateExponent = rsaPrivateKey.getPrivateExponent();
rebuild the private key
RSAPrivateKeySpec rsaPrivateKeySpec = new RSAPrivateKeySpec(modulus, privateExponent);
PrivateKey privateKeyModulusExponent = keyFactory.generatePrivate(rsaPrivateKeySpec);
public key
RSAPublicKey rsaPublicKey = (RSAPublicKey) publicKey;
BigInteger modulusPub = rsaPublicKey.getModulus();
BigInteger publicExponent = rsaPublicKey.getPublicExponent();
rebuild the public key
RSAPublicKeySpec rsaPublicKeySpec = new RSAPublicKeySpec(modulusPub, publicExponent);
PublicKey publicKeyModulusExponent = keyFactory.generatePublic(rsaPublicKeySpec);
System.out.println("\ngenerate private & public key via modulus and private/public exponent");
System.out.println("privateKey Modulus Base64: " + Base64.getEncoder().encodeToString(privateKeyModulusExponent.getEncoded()));
System.out.println("publicKey Modulus Base64: " + Base64.getEncoder().encodeToString(publicKeyModulusExponent.getEncoded()));
System.out.println("\nen-/decryption with original keys");
String plaintext = "this is the message to encrypt";
String ciphertextOriginal = encrypt(publicKey, plaintext);
String decryptedtextOriginal = decrypt(privateKey, ciphertextOriginal);
System.out.println("ciphertext Original : " + ciphertextOriginal);
System.out.println("decryptedtext Original: " + decryptedtextOriginal);
System.out.println("\nen-/decryption with keys from modulus & exponent");
String ciphertextModulus = encrypt(publicKeyModulusExponent, plaintext);
String decryptedtextModulus = decrypt(privateKeyModulusExponent, ciphertextOriginal);
System.out.println("ciphertext Modulus : " + ciphertextModulus);
System.out.println("decryptedtext Modulus : " + decryptedtextModulus);
}
private static String encrypt(PublicKey publicKey, String plaintext) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, IOException, BadPaddingException, IllegalBlockSizeException {
String ciphertext = "";
Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
byte[] ciphertextByte = cipher.doFinal(plaintext.getBytes("UTF8"));
ciphertext = Base64.getEncoder().encodeToString(ciphertextByte).replaceAll("\\r|\\n", "");
return ciphertext;
}
private static String decrypt(PrivateKey privateKey, String ciphertext) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException {
Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.DECRYPT_MODE, privateKey);
byte[] ciphertextByte = Base64.getDecoder().decode(ciphertext);
byte[] decryptedtextByte = cipher.doFinal(ciphertextByte);
return new String(decryptedtextByte);
}
private static String bytesToHex(byte[] bytes) {
StringBuffer result = new StringBuffer();
for (byte b : bytes) result.append(Integer.toString((b & 0xff) + 0x100, 16).substring(1));
return result.toString();
}
}
Source code:
<?php
function encrypt($publicKeyBase64, $plaintext){
$pub = base64_decode($publicKeyBase64);
public key conversion der to pem
$pubPem = chunk_split(base64_encode($pub), 64, "\n");
$pubPem = "-----BEGIN PUBLIC KEY-----\n" . $pubPem . "-----END PUBLIC KEY-----\n";
$ublicKey = "";
$publicKey = openssl_get_publickey($pubPem);
if (!$publicKey) {
echo "Cannot get public key" . "<br>";
}
$ciphertext = "";
openssl_public_encrypt($plaintext, $ciphertext, $publicKey);
if (!empty($ciphertext)) {
openssl_free_key($publicKey);
echo "Encryption OK!" . "<br>";
} else {
echo "Cannot Encrypt" . "<br>";
}
$ciphertextBase64 = base64_encode($ciphertext);
return $ciphertextBase64;
}
function decrypt($privateKeyBase64, $ciphertext){
$pri = base64_decode($privateKeyBase64);
private key conversion der to pem
$priPem = chunk_split(base64_encode($pri), 64, "\n");
$priPem = "-----BEGIN PRIVATE KEY-----\n" . $priPem . "-----END PRIVATE KEY-----\n";
$privateKey = openssl_get_privatekey($priPem);
$Crypted = openssl_private_decrypt($ciphertext, $decryptedtext, $privateKey);
if (!$Crypted) {
echo 'Cannot Decrypt ' . openssl_error_string() . '<br>';
} else {
openssl_free_key($privateKey);
echo "decryptedtext: " . $decryptedtext . "<br>";
}
return $decryptedtext;
}
echo 'php version: ' . PHP_VERSION . ' openssl version: ' . OPENSSL_VERSION_TEXT . '<br>';
$plaintext = "this is the message to encrypt";
echo "plaintext: " . $plaintext . "<br>";
RSA 512 keys from Java GenerateKeysSo.java
echo 'rsa encryption with original keys' . '<br>';
$priBase64 = "MIIBVgIBADANBgkqhkiG9w0BAQEFAASCAUAwggE8AgEAAkEA2wFgcni89ijJ/uijQkzCGF4JiUB1+mEJ48u4Lk0vxB7ym3/FCvOEnN2H7FLUzsGvXRhFriLBiSJlg2tOhV5eiwIDAQABAkEAkDpf4gNRrms+W/ mpSshyKsoDTbh9+d5ePP601QlQI79lrsjdy2GLgk4RV1XmwYinM9Sk8G+ssyXTYHdby6A2wQIhAPcRtl6tub6PFiIE1jcuIkib/ HzAdRYHZx3ZdzRTYDetAiEA4uv43xpGl5N8yG27Kv0DkRoOlr4Ch6oM24hLVw7ClhcCIFgdRAo+MQlqJH2bdf6WAHoez4x6YwepOjhmD2Jk/eK9AiEAtHgI6J5EEB56+gfS+CBa6tZ3Tcl1x6ElMp8Vk/ ooJScCIQDUa3LUkcc58yjJYq8ZNQC/86+HIzd5MldTwg5buR1lpw==";
$pubBase64 = "MFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBANsBYHJ4vPYoyf7oo0JMwhheCYlAdfphCePLuC5NL8Qe8pt/xQrzhJzdh+xS1M7Br10YRa4iwYkiZYNrToVeXosCAwEAAQ==";
echo 'priBase64:' . $priBase64 . '<br>';
echo 'pubBase64:' . $pubBase64 . '<br>';
$ciphertextBase64 = encrypt($pubBase64, $plaintext);
echo 'ciphertext Base64:' . $ciphertextBase64 . '<br>';
$ciphertext = base64_decode($ciphertextBase64);
$decryptedtext = decrypt($priBase64, $ciphertext);
echo "decryptedtext: " . $decryptedtext . "<br><br>";
keys created via modulus & exponent
$priBase64 = "MIGzAgEAMA0GCSqGSIb3DQEBAQUABIGeMIGbAgEAAkEA2wFgcni89ijJ/uijQkzCGF4JiUB1+mEJ48u4Lk0vxB7ym3/FCvOEnN2H7FLUzsGvXRhFriLBiSJlg2tOhV5eiwIBAAJBAJA6X+ IDUa5rPlv5qUrIcirKA024ffneXjz+tNUJUCO/Za7I3cthi4JOEVdV5sGIpzPUpPBvrLMl02B3W8ugNsECAQACAQACAQACAQACAQA=";
$pubBase64 = "MFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBANsBYHJ4vPYoyf7oo0JMwhheCYlAdfphCePLuC5NL8Qe8pt/xQrzhJzdh+xS1M7Br10YRa4iwYkiZYNrToVeXosCAwEAAQ==";
echo 'rsa encryption with keys created via modulus & exponents' . '<br>';
echo 'priBase64:' . $priBase64 . '<br>';
echo 'pubBase64:' . $pubBase64 . '<br>';
$ciphertextBase64 = encrypt($pubBase64, $plaintext);
echo 'ciphertext Base64:' . $ciphertextBase64 . '<br>';
$ciphertext = base64_decode($ciphertextBase64);
$decryptedtext = decrypt($priBase64, $ciphertext);
echo "decryptedtext: " . $decryptedtext . "<br><br>";
echo 'decrypt error: error:0909006C:PEM routines:get_name:no start line' . '<br>';
?>
Final editing of solutions and conclusions
What if we want to use RSA private-key pairs for encryption (and signing?) in systems other than Java. ), then it is very important to save the private key immediately. If we try to reconstruct the private key from the encoded form (via PKCS8EncodedKeySpec), we will definitely lose some data. Those rebuilding private keys will not work (in PHP/openssl).
If we need to
reconstruct the private key from the coded form (byte[]), we need to enhance the key with a method called “createCrtKey”—a method written by President James K. Polk to whom all credits go to us. Since links are sometimes outdated, I’m marking my own answer below as accepted, as the createCrtKey method is documented there.
Thank you to @President James K. Polk, @Topaco, and @michalk for guiding me in the right direction.
Solution
The minimum information required to perform an RSA decryption operation is modulo n and decryption index d. There is an optimization that can be applied to RSA decryption involving the Chinese remainder theorem, where the RSA prime numbers are respectively exponentiated and then combined to produce the final value, so in the RSA Private Key There are some additional fields in syntax for this purpose. and Java public static boolean keyEquals(RSAPrivateCrtKey k1, RSAPrivateCrtKey k2) {
final BigInteger ZERO = BigInteger.ZERO;
boolean result = true;
result = result && isConsistent(k1) && isConsistent(k2);
result = result && k1.getModulus().equals(k2.getModulus());
BigInteger lambda = computeCarmichaelLambda(k1.getPrimeP(), k1.getPrimeQ());
result = result && k1.getPublicExponent().subtract(k2.getPublicExponent()).mod(lambda).equals(ZERO);
result = result && k1.getPrivateExponent().subtract(k2.getPrivateExponent()).mod(lambda).equals(ZERO);
return result;
}
private static boolean isConsistent(RSAPrivateCrtKey k1) {
final BigInteger ZERO = BigInteger.ZERO;
final BigInteger ONE = BigInteger.ONE;
BigInteger n = k1.getModulus();
BigInteger p = k1.getPrimeP();
BigInteger q = k1.getPrimeQ();
BigInteger e = k1.getPublicExponent();
BigInteger d = k1.getPrivateExponent();
boolean result = true;
result = p.multiply(q).equals(n);
BigInteger lambda = computeCarmichaelLambda(p, q);
result = result && e.multiply(d).mod(lambda).equals(ONE);
result = result && d.subtract(key.getPrimeExponentP()).mod(p.subtract(ONE)).equals(ZERO);
result = result && d.subtract(key.getPrimeExponentQ()).mod(q.subtract(ONE)).equals(ZERO);
result = result && q.multiply(k1.getCrtCoefficient()).mod(p).equals(ONE);
return result;
}
private static BigInteger computeCarmichaelLambda(BigInteger p, BigInteger q) {
return lcm(p.subtract(BigInteger.ONE), q.subtract(BigInteger.ONE));
}
private static BigInteger lcm(BigInteger x, BigInteger y) {
return x.multiply(y).divide(x.gcd(y));
}