Convert JAVA program to PHP

I want someone to convert JAVA program to encrypt aadhar number i.e 12 digit number with Public Key using following process. and please check on sandbox api. link is given below.

Encryption process for aadhar parameter:
1.Decode public key using base64 encoding technique
2.Compute RSA encrypted signature using decoded key and message.
3.Encode encrypted signature with base64 encoding to send message on API

Public Key for UAT : MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCaFyrzeDhMaFLx+LZUNOOO14Pj9aPfr+1WOanDgDHxo9NekENYcWUftM9Y17ul2pXr3bqw0GCh4uxNoTQ5cTH4buI42LI8ibMaf7Kppq9MzdzI9/7pOffgdSn+P8J64CJAk3VrVswVgfy8lABt7fL8R6XReI9x8ewwKHhCRTwBgQIDAQAB

JAVA Program:
public static String calculateRSA( String salt ) throws InvalidKeyException, Exception {

Cipher encryptCipher = Cipher.getInstance("RSA");
encryptCipher.init(Cipher.ENCRYPT_MODE, getPublicKey());
byte[] secretMessageBytes = salt.getBytes("UTF-8");
byte[] encryptedMessageBytes = encryptCipher.doFinal(secretMessageBytes);
String encodedMessage = Base64.encodeBase64String(encryptedMessageBytes);
return encodedMessage;
}
public static PublicKey getPublicKey() throws Exception {
String rawPublicKey = "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCaFyrzeDhMaFLx+LZUNOOO14Pj9aPfr+1WOanDgDHxo9NekENYcWUftM9Y17ul2pXr3bqw0GCh4uxNoTQ5cTH4buI42LI8ibMaf7Kppq9MzdzI9/7pOffgdSn+P8J64CJAk3VrVswVgfy8lABt7fL8R6XReI9x8ewwKHhCRTwBgQIDAQAB";
byte[] keyBytes = Base64.decodeBase64(rawPublicKey);
X509EncodedKeySpec spec = new X509EncodedKeySpec(keyBytes);
KeyFactory kf = KeyFactory.getInstance("RSA");
return kf.generatePublic(spec);// generatePrivate(spec);
}

Reference URL: https://developers.eko.in/reference#aeps-transaction-api