How can I construct a java.security.PublicKey object from a base64 encoded string?

Question

I have a bse64encoded string Public key from external source (Android Store) and I need to use it to verify signed content. How can I convert the string into an instance of the java.security.PublicKey interface. I am on Java 6 if that makes a difference.

The key is (probably) generated using standard java lib and not bouncy castle (its from a remote team so I am not sure). Their sample code says to use Security.generatePublicKey(base64EncodedPublicKey); but the Security object in standard java has no such method.

What are you using to create your key, the standard java libary, BouncyCastle or something else? — James Black, Jun 05 '12 at 16:04
Standard java very probably but its a remote team so I am not sure — Usman Ismail, Jun 05 '12 at 16:18

alexis · Answer 1 · 2014-07-04T16:05:41.167

76

Code for the above answer

public static PublicKey getKey(String key){
    try{
        byte[] byteKey = Base64.decode(key.getBytes(), Base64.DEFAULT);
        X509EncodedKeySpec X509publicKey = new X509EncodedKeySpec(byteKey);
        KeyFactory kf = KeyFactory.getInstance("RSA");

        return kf.generatePublic(X509publicKey);
    }
    catch(Exception e){
        e.printStackTrace();
    }

    return null;
}

edited Jul 04 '14 at 16:05

answered Jul 01 '14 at 03:59

alexis

1,081
1
9
7

I was using a similar piece of code, but this is better ;) Also if working on android you could use: byte[] byteKey = Base64.decode(key.getBytes(), Base64.DEFAULT); – tozhan Jul 03 '14 at 22:06
@Hooli: It's "android.util.Base64". Anyway, the value of DEFAULT is 0. – nonzaprej Mar 17 '17 at 12:12
6

Obviously, you can you Base64.getDecoder().decode(bytes) method from java.util. – pzeszko Apr 25 '17 at 19:09
6

I modified the first line like this to make it work in Java 8 `byte[] byteKey = Base64.getDecoder().decode(key.getBytes());` – mico Jul 26 '18 at 12:36

score 30 · Accepted Answer · answered Jun 05 '12 at 18:35

30

Ok for grins ... try this

base64 decode the key data to get a byte array (byte[])
Create a new X509EncodedKeySpec using the byte array
Get an instance of KeyFactory using KeyFactory.getInstance("RSA") assuming RSA here
call the method generatePublic(KeySpec) with the X509EncodedKeySpec
Result /should/ be a public key for your usage.

answered Jun 05 '12 at 18:35

Dave G

9,639
36
41

1

Had same issue, tried this and got this exception `java.security.spec.InvalidKeySpecException: java.security.InvalidKeyException: invalid key format` – Wafula Samuel Feb 21 '20 at 13:52
I get the same exception. I tried removineding the "BEGIN and END CERTIFICATE" and still get the same error. – testing123 Oct 22 '20 at 23:12
As this solved for the requestor's situation, please ask a new question on stackoverflow and provide link here. Please provide code examples of what you are doing and utilize an example certificate e.g. http://fm4dd.com/openssl/source/PEM/certs/2048b-rsa-example-cert.pem. Ideally, sign up for a github account and provide a link to the repository containing your exemplar code and test certificate. – Dave G Oct 23 '20 at 11:40

score 3 · Answer 3 · answered May 26 '17 at 14:52

Try this....

PublicKey getPublicKey(byte[] encodedKey) throws NoSuchAlgorithmException, InvalidKeySpecException
{
    KeyFactory factory = KeyFactory.getInstance("RSA");
    X509EncodedKeySpec encodedKeySpec = new X509EncodedKeySpec(encodedKey);
    return factory.generatePublic(encodedKeySpec);
}

score 1 · Answer 4 · answered Jun 28 '21 at 05:59

Here's a code snippet:

import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.NoSuchAlgorithmException;
import java.security.PublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.RSAPublicKeySpec;

import org.apache.commons.codec.binary.Base64;
try {
    KeyFactory kf = KeyFactory.getInstance("RSA");
    BigInteger modulus = new BigInteger(1, Base64.decodeBase64(this.stringValue("n")));
    BigInteger exponent = new BigInteger(1, Base64.decodeBase64(this.stringValue("e")));
    return kf.generatePublic(new RSAPublicKeySpec(modulus, exponent));
} catch (InvalidKeySpecException var4) {
    throw new InvalidPublicKeyException("Invalid public key", var4);
} catch (NoSuchAlgorithmException var5) {
    throw new InvalidPublicKeyException("Invalid algorithm to generate key", var5);
}

although not what the question asked, this works well if you have the JWK or have the PEM to convert to JWK online — Samuel Dominguez, Dec 13 '22 at 04:09

score 0 · Answer 5 · answered Jun 21 '18 at 10:04

Using spongy castle

public static PublicKey getPublicKeyFromString(String key) throws Exception {
    KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);
    org.spongycastle.asn1.pkcs.RSAPublicKey pkcs1PublicKey
            = org.spongycastle.asn1.pkcs.RSAPublicKey.getInstance(decodeB64(key));
    RSAPublicKeySpec keySpec
            = new RSAPublicKeySpec(pkcs1PublicKey.getModulus(), pkcs1PublicKey.getPublicExponent());
    PublicKey publicKey = keyFactory.generatePublic(keySpec);
    return publicKey;
}

score 0 · Answer 6 · edited Nov 15 '22 at 16:17

you can try this solution:

add this dependency:

<dependency>
    <groupId>org.bouncycastle</groupId>
    <artifactId>bcpkix-jdk15on</artifactId>
    <version>1.70</version>
</dependency>

and use this method:

private Key parsePublicKey(String publicKey) throws IOException {
    try (StringReader sr = new StringReader(publicKey)) {
        PEMParser parser = new PEMParser(sr);
        JcaPEMKeyConverter converter = new JcaPEMKeyConverter();
        SubjectPublicKeyInfo publicKeyInfo = SubjectPublicKeyInfo.getInstance(parser.readObject());
        return converter.getPublicKey(publicKeyInfo);
    } catch (IOException e) {
        // handle me
    }
}

How can I construct a java.security.PublicKey object from a base64 encoded string?

6 Answers6

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