Convert String to RSA Private key in Android

Question

in Android i use below code to convert String to RSA private key. this code work when i use this site for String private key

https://www.devglan.com/online-tools/rsa-encryption-decryption

but when i use this site , my code dose not work.

https://8gwifi.org/RSAFunctionality?keysize=1024

my code in Android studio is :

public static PrivateKey stringToPrivateKey(String privateKeyString)
    {
        try {
            if (privateKeyString.contains("-----BEGIN PRIVATE KEY-----") || privateKeyString.contains("-----END PRIVATE KEY-----"))
                privateKeyString = privateKeyString.replace("-----BEGIN PRIVATE KEY-----", "").replace("-----END PRIVATE KEY-----", "");


            if (privateKeyString.contains("-----BEGIN RSA PRIVATE KEY-----") || privateKeyString.contains("-----END RSA PRIVATE KEY-----"))
                privateKeyString = privateKeyString.replace("-----BEGIN RSA PRIVATE KEY-----", "").replace("-----END RSA PRIVATE KEY-----", "");

            privateKeyString.trim();
            privateKeyString = privateKeyString.replaceAll("\\s+","");
            privateKeyString = privateKeyString.replaceAll("\\r+","");
            privateKeyString = privateKeyString.replaceAll("^ | $|\\n ", "");


            byte[] keyBytes = Base64.decode(privateKeyString, Base64.DEFAULT);
            PKCS8EncodedKeySpec spec = new PKCS8EncodedKeySpec(keyBytes);
            KeyFactory keyFactory = KeyFactory.getInstance(RSA);
            return keyFactory.generatePrivate( spec);

        } catch (NoSuchAlgorithmException | InvalidKeySpecException e) {
            e.printStackTrace();
        }
    }

with second link Error is in this line

keyFactory.generatePrivate( spec);

That's correct. The second site creates keys that use a format that is not supported by android. So don't use that site. — President James K. Polk, Aug 08 '19 at 00:40
@james-k-polk i need use second site key for my android.how can i do that? — m-tech, Aug 09 '19 at 22:36
Follow the links given in [this answer](https://stackoverflow.com/a/55676541/238704) — President James K. Polk, Aug 09 '19 at 22:47

score 0 · Accepted Answer · edited Jun 20 '20 at 09:12

This code solve my problem:

void dear(String publicKeyB64)  throws NoSuchAlgorithmException, InvalidKeySpecException{

        if (publicKeyB64.contains("-----BEGIN PUBLIC KEY-----") || publicKeyB64.contains("-----END PUBLIC KEY-----"))
            publicKeyB64 = publicKeyB64.replace("-----BEGIN PUBLIC KEY-----", "").replace("-----END PUBLIC KEY-----", "");
        if (publicKeyB64.contains("-----BEGIN RSA PUBLIC KEY-----") || publicKeyB64.contains("-----END RSA PUBLIC KEY-----"))
            publicKeyB64 = publicKeyB64.replace("-----BEGIN RSA PUBLIC KEY-----", "").replace("-----END RSA PUBLIC KEY-----", "");

        // ok, you may need to use the Base64 decoder of bouncy or Android instead
        try{
            byte[] decoded = Base64.decode(publicKeyB64, Base64.DEFAULT);
            org.bouncycastle.asn1.pkcs.RSAPublicKey pkcs1PublicKey = org.bouncycastle.asn1.pkcs.RSAPublicKey.getInstance(decoded);
            BigInteger modulus = pkcs1PublicKey.getModulus();
            BigInteger publicExponent = pkcs1PublicKey.getPublicExponent();
            RSAPublicKeySpec keySpec = new RSAPublicKeySpec(modulus, publicExponent);
            KeyFactory kf = KeyFactory.getInstance("RSA");
            PublicKey generatedPublic = kf.generatePublic(keySpec);
            uk =generatedPublic;
           //uk is public variable in class and means public key
        }
        catch (Exception e){
            Log.i("your log","errro in dear function");
        }

    }

And this is my library:

compile "org.bouncycastle:bcprov-jdk15on:1.58"

compile "org.bouncycastle:bcpkix-jdk15on:1.58"

Convert String to RSA Private key in Android

1 Answers1