Class RSA

java.lang.Object
  |
  +--RSA

public class RSA

extends java.lang.Object

Program to encrypt and decrypt files using the RSA algorithm. This program accepts arguments from the command line and can be run in 3 ways:

• java RSA -mk [username] : create a pair of public and private key, and a modulus for this username, and stores them in 3 files in the local directory.
• java RSA -e [username] [message_file] [encoded_file] : uses the private key of username to crypt the file message_file. The crypted message is stored in the file encoded_file.
• java RSA -d [username] [encoded_file] [message_file] : uses the public key of username to decrypt the file encoded_file. The resulting clear file is stored in encoded_file.

RSA uses the functions implemented in class Math. The keys are large prime of 1024 bits.

Author:

E.Lemonnier & E.Nordenstam

Field Summary

static int

SIZE_KEY

Constructor Summary

RSA()

Method Summary

static java.math.BigInteger	decrypt(java.math.BigInteger cypher, java.math.BigInteger key, java.math.BigInteger modulus) Decrypt a message with RSA.
static java.math.BigInteger	encrypt(java.math.BigInteger message, java.math.BigInteger key, java.math.BigInteger modulus) Encrypt a message with RSA.
static java.math.BigInteger[]	keys() Generate a pair of private and public keys, and a modulus.
static void	main(java.lang.String[] arg) Crypt/Decrypt a file, or generate keys for a user.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

SIZE_KEY

public static final int SIZE_KEY

Constructor Detail

RSA

public RSA()

Method Detail

main

public static void main(java.lang.String[] arg)

Crypt/Decrypt a file, or generate keys for a user. See on top of this page for a detailed description.

Parameters:

see - the description above.

encrypt

public static java.math.BigInteger encrypt(java.math.BigInteger message,
                                           java.math.BigInteger key,
                                           java.math.BigInteger modulus)

Encrypt a message with RSA. In fact compute message ^ key mod modulus.

Parameters:

message - the message to encrypt.

key - the key used to crypt the message.

modulus - key modulus.

Returns:

the encoded message.

decrypt

public static java.math.BigInteger decrypt(java.math.BigInteger cypher,
                                           java.math.BigInteger key,
                                           java.math.BigInteger modulus)

Decrypt a message with RSA. In fact compute cypher ^ key mod modulus.

Parameters:

cypher - the cypher to decrypt.

key - the key used to crypt the message.

modulus - key modulus.

Returns:

the decrypted message.

keys

public static java.math.BigInteger[] keys()

Generate a pair of private and public keys, and a modulus. The result is an array of BigIntegers of this form: [private_key, public_key, modulus].

Returns:

the 2 keys and the modulus.