RSA decrypt - Java Security

Java examples for Security:RSA

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Description

RSA decrypt

Demo Code


import javax.crypto.Cipher;
import java.io.ByteArrayOutputStream;
import java.security.KeyFactory;
import java.security.Signature;
import java.security.interfaces.RSAPrivateCrtKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;

public class Main{
    public byte[] decrypt(byte[] secret) {
        if (privateKey == null) {
            throw new RuntimeException("private key is null.");
        }/*w w  w .ja  v  a 2 s . co m*/
        try {
            Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
            cipher.init(Cipher.DECRYPT_MODE, privateKey);
            int size = privateKey.getModulus().bitLength() / 8;
            ByteArrayOutputStream baos = new ByteArrayOutputStream(
                    (secret.length + size - 12) / (size - 11) * size);
            int left = 0;
            for (int i = 0; i < secret.length;) {
                left = secret.length - i;
                if (left > size) {
                    cipher.update(secret, i, size);
                    i += size;
                } else {
                    cipher.update(secret, i, left);
                    i += left;
                }

                baos.write(cipher.doFinal());
            }

            return baos.toByteArray();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
    public static byte[] decrypt(byte[] secret, byte[] privateKey) {
        return new RsaHelper(null, privateKey).decrypt(secret);
    }
}

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