How to read .pem file to get private and public key
I am writing a small piece of code which reads public and private key stored in .pem file. I am using the following commands to generate the keys.
Below command to generate pair of key.
$openssl genrsa -out mykey.pem 2048
This command to generate the private key
$openssl pkcs8 -topk8 -inform PEM -outform PEM -in mykey.pem \
-out private_key.pem -nocrypt
and this command to get the public key.
$ openssl rsa -in mykey.pem -pubout -outform DER -out public_key.der
I have written two methods which reads the private key and public key respectively.
public PrivateKey getPemPrivateKey(String filename, String algorithm) throws Exception {
File f = new File(filename);
FileInputStream fis = new FileInputStream(f);
DataInputStream dis = new DataInputStream(fis);
byte[] keyBytes = new byte[(int) f.length()];
dis.readFully(keyBytes);
dis.close();
String temp = new String(keyBytes);
String privKeyPEM = temp.replace("-----BEGIN PRIVATE KEY-----\n", "");
privKeyPEM = privKeyPEM.replace("-----END PRIVATE KEY-----", "");
//System.out.println("Private key\n"+privKeyPEM);
Base64 b64 = new Base64();
byte [] decoded = b64.decode(privKeyPEM);
PKCS8EncodedKeySpec spec = new PKCS8EncodedKeySpec(decoded);
KeyFactory kf = KeyFactory.getInstance(algorithm);
return kf.generatePrivate(spec);
}
public PublicKey getPemPublicKey(String filename, String algorithm) throws Exception {
File f = new File(filename);
FileInputStream fis = new FileInputStream(f);
DataInputStream dis = new DataInputStream(fis);
byte[] keyBytes = new byte[(int) f.length()];
dis.readFully(keyBytes);
dis.close();
String temp = new String(keyBytes);
String publicKeyPEM = temp.replace("-----BEGIN PUBLIC KEY-----\n", "");
publicKeyPEM = publicKeyPEM.replace("-----END PUBLIC KEY-----", "");
Base64 b64 = new Base64();
byte [] decoded = b64.decode(publicKeyPEM);
X509EncodedKeySpec spec =
new X509EncodedKeySpec(decoded);
KeyFactory kf = KeyFactory.getInstance(algorithm);
return kf.generatePublic(spec);
}
I feel like this is a naive way of doing it. I couldn't get any better way of doing it over internet. Can anyone suggest me what is the best way of writing the same code to handle the generic cases. I don' want to use any kind of third party library.
I have very basic knowledge of singing/encrypting and hardly use any java security APIs. So if I am not making sense somewhere then please point out.
Solution 1:
Try this class.
package groovy;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.security.GeneralSecurityException;
import java.security.InvalidKeyException;
import java.security.KeyFactory;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.Signature;
import java.security.SignatureException;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import javax.crypto.Cipher;
import org.apache.commons.codec.binary.Base64;
public class RSA {
private static String getKey(String filename) throws IOException {
// Read key from file
String strKeyPEM = "";
BufferedReader br = new BufferedReader(new FileReader(filename));
String line;
while ((line = br.readLine()) != null) {
strKeyPEM += line + "\n";
}
br.close();
return strKeyPEM;
}
public static RSAPrivateKey getPrivateKey(String filename) throws IOException, GeneralSecurityException {
String privateKeyPEM = getKey(filename);
return getPrivateKeyFromString(privateKeyPEM);
}
public static RSAPrivateKey getPrivateKeyFromString(String key) throws IOException, GeneralSecurityException {
String privateKeyPEM = key;
privateKeyPEM = privateKeyPEM.replace("-----BEGIN PRIVATE KEY-----\n", "");
privateKeyPEM = privateKeyPEM.replace("-----END PRIVATE KEY-----", "");
byte[] encoded = Base64.decodeBase64(privateKeyPEM);
KeyFactory kf = KeyFactory.getInstance("RSA");
PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(encoded);
RSAPrivateKey privKey = (RSAPrivateKey) kf.generatePrivate(keySpec);
return privKey;
}
public static RSAPublicKey getPublicKey(String filename) throws IOException, GeneralSecurityException {
String publicKeyPEM = getKey(filename);
return getPublicKeyFromString(publicKeyPEM);
}
public static RSAPublicKey getPublicKeyFromString(String key) throws IOException, GeneralSecurityException {
String publicKeyPEM = key;
publicKeyPEM = publicKeyPEM.replace("-----BEGIN PUBLIC KEY-----\n", "");
publicKeyPEM = publicKeyPEM.replace("-----END PUBLIC KEY-----", "");
byte[] encoded = Base64.decodeBase64(publicKeyPEM);
KeyFactory kf = KeyFactory.getInstance("RSA");
RSAPublicKey pubKey = (RSAPublicKey) kf.generatePublic(new X509EncodedKeySpec(encoded));
return pubKey;
}
public static String sign(PrivateKey privateKey, String message) throws NoSuchAlgorithmException, InvalidKeyException, SignatureException, UnsupportedEncodingException {
Signature sign = Signature.getInstance("SHA1withRSA");
sign.initSign(privateKey);
sign.update(message.getBytes("UTF-8"));
return new String(Base64.encodeBase64(sign.sign()), "UTF-8");
}
public static boolean verify(PublicKey publicKey, String message, String signature) throws SignatureException, NoSuchAlgorithmException, UnsupportedEncodingException, InvalidKeyException {
Signature sign = Signature.getInstance("SHA1withRSA");
sign.initVerify(publicKey);
sign.update(message.getBytes("UTF-8"));
return sign.verify(Base64.decodeBase64(signature.getBytes("UTF-8")));
}
public static String encrypt(String rawText, PublicKey publicKey) throws IOException, GeneralSecurityException {
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
return Base64.encodeBase64String(cipher.doFinal(rawText.getBytes("UTF-8")));
}
public static String decrypt(String cipherText, PrivateKey privateKey) throws IOException, GeneralSecurityException {
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.DECRYPT_MODE, privateKey);
return new String(cipher.doFinal(Base64.decodeBase64(cipherText)), "UTF-8");
}
}
Required jar library "common-codec-1.6"
Solution 2:
Java 9+:
private byte[] loadPEM(String resource) throws IOException {
URL url = getClass().getResource(resource);
InputStream in = url.openStream();
String pem = new String(in.readAllBytes(), StandardCharsets.ISO_8859_1);
Pattern parse = Pattern.compile("(?m)(?s)^---*BEGIN.*---*$(.*)^---*END.*---*$.*");
String encoded = parse.matcher(pem).replaceFirst("$1");
return Base64.getMimeDecoder().decode(encoded);
}
@Test
public void test() throws Exception {
KeyFactory kf = KeyFactory.getInstance("RSA");
CertificateFactory cf = CertificateFactory.getInstance("X.509");
PrivateKey key = kf.generatePrivate(new PKCS8EncodedKeySpec(loadPEM("test.key")));
PublicKey pub = kf.generatePublic(new X509EncodedKeySpec(loadPEM("test.pub")));
Certificate crt = cf.generateCertificate(getClass().getResourceAsStream("test.crt"));
}
Java 8:
replace the in.readAllBytes() call with a call to this:
byte[] readAllBytes(InputStream in) throws IOException {
ByteArrayOutputStream baos= new ByteArrayOutputStream();
byte[] buf = new byte[1024];
for (int read=0; read != -1; read = in.read(buf)) { baos.write(buf, 0, read); }
return baos.toByteArray();
}
thanks to Daniel for noticing API compatibility issues