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+The RC4 library.
+RC4 is a stream cipher that operates on a byte stream.  It can be used with
+any length key but I would recommend normally using 16 bytes.
+
+This library requires the inclusion of 'rc4.h'.
+
+The RC4 encryption function takes what is called an RC4_KEY as an argument.
+The RC4_KEY is generated by the RC4_set_key function from the key bytes.
+
+RC4, being a stream cipher, does not have an encryption or decryption mode.
+It produces a stream of bytes that the input stream is xor'ed against and
+so decryption is just a case of 'encrypting' again with the same key.
+
+I have only put in one 'mode' for RC4 which is the normal one.  This means
+there is no initialisation vector and there is no feedback of the cipher
+text into the cipher.  This implies that you should not ever use the
+same key twice if you can help it.  If you do, you leave yourself open to
+known plain text attacks; if you know the plain text and
+corresponding cipher text in one message, all messages that used the same
+key can have the cipher text decoded for the corresponding positions in the
+cipher stream.
+
+The main positive feature of RC4 is that it is a very fast cipher; about 4
+times faster that DES.  This makes it ideally suited to protocols where the
+key is randomly chosen, like SSL.
+
+The functions are as follows:
+
+void RC4_set_key(
+RC4_KEY *key;
+int len;
+unsigned char *data);
+	This function initialises the RC4_KEY structure with the key passed
+	in 'data', which is 'len' bytes long.  The key data can be any
+	length but 16 bytes seems to be a good number.
+
+void RC4(
+RC4_KEY *key;
+unsigned long len;
+unsigned char *in;
+unsigned char *out);
+	Do the actual RC4 encryption/decryption.  Using the 'key', 'len'
+	bytes are transformed from 'in' to 'out'.  As mentioned above,
+	decryption is the operation as encryption.