4.8 Java Code to Encrypt and Decrypt a Sample Client Random
The following Java code illustrates how to encrypt and decrypt with RSA.
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import java.math.BigInteger; public class RdpRsaEncrypt { // // Print out the contents of a byte array in hexadecimal. // private static void PrintBytes( byte[] bytes ) { int cBytes = bytes.length; int iByte = 0; for (;;) { for (int i = 0; i < 8; i++) { String hex = Integer.toHexString(bytes[iByte++] & 0xff); if (hex.length() == 1) { hex = "0" + hex; } System.out.print("0x" + hex + " "); if (iByte >= cBytes) { System.out.println(); return; } } System.out.println(); } } // // Reverse the order of the values in a byte array. // public static void ReverseByteArray( byte[] array ) { int i, j; byte temp; for (i = 0, j = array.length - 1; i < j; i++, j--) { temp = array[i]; array[i] = array[j]; array[j] = temp; } } // // Use RSA to encrypt data. // public static byte[] RsaEncrypt( byte[] modulusBytes, byte[] exponentBytes, byte[] dataBytes ) { // // Reverse the passed in byte arrays and then use these to // create the BigIntegers for the RSA computation. // ReverseByteArray(modulusBytes); ReverseByteArray(exponentBytes); ReverseByteArray(dataBytes); BigInteger modulus = new BigInteger( 1, modulusBytes ); BigInteger exponent = new BigInteger( 1, exponentBytes ); BigInteger data = new BigInteger( 1, dataBytes ); // // Perform RSA encryption: // ciphertext = plaintext^exponent % modulus. // BigInteger cipherText = data.modPow( exponent, modulus ); // // Reverse the generated ciphertext. // byte[] cipherTextBytes = cipherText.toByteArray(); ReverseByteArray(cipherTextBytes); // // Undo the reversal of the passed in byte arrays. // ReverseByteArray(modulusBytes); ReverseByteArray(exponentBytes); ReverseByteArray(dataBytes); return cipherTextBytes; } // // Use RSA to decrypt data. // public static byte[] RsaDecrypt( byte[] modulusBytes, byte[] privateExponentBytes, byte[] encryptedDataBytes ) { // // Reverse the passed in byte arrays and then use these to // create the BigIntegers for the RSA computation. // ReverseByteArray(modulusBytes); ReverseByteArray(privateExponentBytes); ReverseByteArray(encryptedDataBytes); BigInteger modulus = new BigInteger( 1, modulusBytes ); BigInteger privateExponent = new BigInteger( 1, privateExponentBytes ); BigInteger encryptedData = new BigInteger( 1, encryptedDataBytes ); // // Perform RSA encryption: // plaintext = ciphertext^privateExponent % modulus. // BigInteger decryptedData = encryptedData.modPow( privateExponent, modulus ); // // Reverse the generated plaintext. // byte[] decryptedDataBytes = decryptedData.toByteArray(); ReverseByteArray(decryptedDataBytes); // // Undo the reversal of the passed in byte arrays. // ReverseByteArray(modulusBytes); ReverseByteArray(privateExponentBytes); ReverseByteArray(encryptedDataBytes); return decryptedDataBytes; } // // Main routine. // public static void main( String[] args ) { // // Modulus bytes obtained straight from the wire in the // proprietary certificate (in little endian format). // This is for a 512-bit key set. // byte[] modulusBytes = { (byte) 0x37, (byte) 0xa8, (byte) 0x70, (byte) 0xfe, (byte) 0x9a, (byte) 0xb9, (byte) 0xa8, (byte) 0x54, (byte) 0xcb, (byte) 0x98, (byte) 0x79, (byte) 0x44, (byte) 0x7a, (byte) 0xb9, (byte) 0xeb, (byte) 0x38, (byte) 0x06, (byte) 0xea, (byte) 0x26, (byte) 0xa1, (byte) 0x47, (byte) 0xea, (byte) 0x19, (byte) 0x70, (byte) 0x5d, (byte) 0xf3, (byte) 0x52, (byte) 0x88, (byte) 0x70, (byte) 0x21, (byte) 0xb5, (byte) 0x9e, (byte) 0x50, (byte) 0xb4, (byte) 0xe1, (byte) 0xf5, (byte) 0x1a, (byte) 0xd8, (byte) 0x2d, (byte) 0x51, (byte) 0x4d, (byte) 0x1a, (byte) 0xad, (byte) 0x79, (byte) 0x7c, (byte) 0x89, (byte) 0x46, (byte) 0xb0, (byte) 0xcc, (byte) 0x66, (byte) 0x74, (byte) 0x02, (byte) 0xd8, (byte) 0x28, (byte) 0x5d, (byte) 0x9d, (byte) 0xd7, (byte) 0xca, (byte) 0xfc, (byte) 0x60, (byte) 0x0f, (byte) 0x38, (byte) 0xf9, (byte) 0xb3 }; // // Exponent bytes (in little endian order) obtained straight // from the wire (in the proprietary certificate). // byte[] exponentBytes = { (byte) 0x01, (byte) 0x00, (byte) 0x01, (byte) 0x00 }; // // Private exponent of the private key generated by the // server (in little endian format). // byte[] privateExponentBytes = { (byte) 0xc1, (byte) 0x07, (byte) 0xe7, (byte) 0xd4, (byte) 0xd3, (byte) 0x38, (byte) 0x8d, (byte) 0x36, (byte) 0xf5, (byte) 0x9e, (byte) 0x8b, (byte) 0x96, (byte) 0x0d, (byte) 0x55, (byte) 0x65, (byte) 0x08, (byte) 0x28, (byte) 0x25, (byte) 0xa3, (byte) 0x2e, (byte) 0xc7, (byte) 0x68, (byte) 0xd6, (byte) 0x44, (byte) 0x85, (byte) 0x2d, (byte) 0x32, (byte) 0xf6, (byte) 0x72, (byte) 0xa8, (byte) 0x9b, (byte) 0xba, (byte) 0x5e, (byte) 0x82, (byte) 0x82, (byte) 0xf0, (byte) 0x5c, (byte) 0x0c, (byte) 0xeb, (byte) 0x6b, (byte) 0x12, (byte) 0x6a, (byte) 0xa7, (byte) 0x45, (byte) 0x15, (byte) 0xce, (byte) 0x41, (byte) 0xe0, (byte) 0x03, (byte) 0xe5, (byte) 0xe6, (byte) 0x6d, (byte) 0xdf, (byte) 0xfd, (byte) 0x58, (byte) 0x61, (byte) 0x0b, (byte) 0x07, (byte) 0xa4, (byte) 0x7b, (byte) 0xb3, (byte) 0xf3, (byte) 0x71, (byte) 0x94 }; // // Sample 32-byte client random. // byte[] clientRandomBytes = { (byte) 0xff, (byte) 0xee, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0xff }; System.out.println("Client random:"); PrintBytes(clientRandomBytes); // // Perform encryption. // byte[] encryptedClientRandomBytes = RsaEncrypt( modulusBytes, exponentBytes, clientRandomBytes ); System.out.println("Encrypted client random:"); PrintBytes(encryptedClientRandomBytes); // // Perform decryption. // byte[] decryptedClientRandomBytes = RsaDecrypt( modulusBytes, privateExponentBytes, encryptedClientRandomBytes ); System.out.println("Decrypted client random:"); PrintBytes(decryptedClientRandomBytes); } };