How to convert from String to PublicKey?

Question

I've used the following code to convert the public and private key to a string

KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA"); keyPairGen.initialize(2048); KeyPair keyPair = keyPairGen.genKeyPair(); PublicKey publicKey = keyPair.getPublic(); PrivateKey privateKey = keyPair.getPrivate(); String publicK = Base64.encodeBase64String(publicKey.getEncoded()); String privateK = Base64.encodeBase64String(privateKey.getEncoded());

Now I'm trying to convert it back to public ad private key

PublicKey publicDecoded = Base64.decodeBase64(publicK);

I'm getting error of cannot convert from byte[] to public key. So I tried like this

PublicKey publicDecoded = new SecretKeySpec(Base64.decodeBase64(publicK),"RSA");

This leads to error like below

java.security.spec.InvalidKeySpecException: java.security.InvalidKeyException: Neither a public nor a private key

Looks like I'm doing wrong key conversion here. Any help would be appreciated.

possible duplicate of Load stored RSA public/private key from disk? — Artjom B.
– Artjom B., Commented Feb 3, 2015 at 8:51
possible duplicate of Converting Strings to encryption keys and vice versa java — Sufiyan Ghori
– Sufiyan Ghori, Commented Feb 3, 2015 at 8:54
Thanks guys. Now I'm able to successfully convert it back to PublicKey using X509EncodedKeySpec. I do searched before posting the question, but what I've seen was mostly involves conversion of SecretKey but not public and private keys. — The Coder
– The Coder, Commented Feb 3, 2015 at 9:00

weston · Accepted Answer · 2015-02-03 09:03:20Z

52

I don't think you can use the SecretKeySpec with RSA.

This should do:

byte[] publicBytes = Base64.decodeBase64(publicK); X509EncodedKeySpec keySpec = new X509EncodedKeySpec(publicBytes); KeyFactory keyFactory = KeyFactory.getInstance("RSA"); PublicKey pubKey = keyFactory.generatePublic(keySpec);

And to decode the private use PKCS8EncodedKeySpec

answered Feb 3, 2015 at 9:03

weston

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7 Comments

The Coder Over a year ago

thanks. I forgot about private key. I'll use PKCS8EncodedKeySpec for private key.

Hooli Over a year ago

Which import does the above Base64 come from?

gybandi Over a year ago

@Hooli I think it's from org.apache.commons.codec.binary.Base64. also, you could use Base64.getDecoder().decode(publicK) in the java.util if you use Java 1.8

Haya Raed Over a year ago

I am trying to do the same thing but am getting java.security.spec.InvalidKeySpecException: java.security.InvalidKeyException ... when it tries to execute the last line .. keyfactory.generatePublic(keySpec)

weston Over a year ago

@HayaRaed ask a new question, you'll get far more attention.

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