Des Des package contains the Des extension module for Perl.
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Des package contains the Des extension module for Perl. Des package contains the Des extension module for Perl.The Des extension module gives access to the DES library.The following is a brief and over-simplified description of the relevant stuff about DES.DES keys are 8-byte blocks. A key is passed to a perl function as an 8-byte string. Before keys can be used to encrypt or decrypt data, the key needs to be transformed into a key schedule using the function set_key. There is a certain amount of overhead in creating these key schedules (which are 128 bytes or 256 bytes depending on implementation and architecture) so they can be created and cached for later if desired. Encryption and decryption can be done in 3 modes:ECB (electronic code book) modeTakes a des_cblock (perl 8-byte string) and produces another des_cblock. (Very rarely useful for large amounts of plain text, subject to known plaintext attacks under certain circumstances, only slightly faster than CBC or PCBC mode, and you lose even this advantage in perl).CBC (cipher block chaining) modeTakes an arbitrary length string, pads it out (internally) on the right with NULs to a multiple of 8-bytes. Encrypts/decrypts the data and produces output (same size as padded input) which is an exact multiple of 8 bytes long. Changing a single bit of the cleartext affects all the following ciphertext. However, changing a single bit of the ciphertext affects only the corresponding cleartext block and the following block. This is occasionally an advantage but is usually a disadvantage.PCBC modeA modified CBC mode with indefinite proagation of single bit errors both from cleartext to ciphertext and from ciphertext to cleartext. "Usually" the best mode (for certain values of "usually").Functions imported by use Des.string_to_key (STRING)Takes an arbitrary STRING and munges it (with a one-way function) into a DES key, which is returned.set_key (KEY)The DES key KEY (which must be a string of exactly 8 bytes) is turned into a key schedule which is returned.ecb_encrypt (INPUT, SCHEDULE)The INPUT argument (which must be a string of exactly 8 bytes) is encrypted using ECB mode using key schedule SCHEDULE (created using set_key) and the resulting 8-byte string is returned.ecb_decrypt (INPUT, SCHEDULE)The INPUT argument (which must be a string of exactly 8 bytes) is decrypted using ECB mode using key schedule SCHEDULE (created using set_key) and the resulting 8-byte string is returned.cbc_encrypt (INPUT, OUTPUT, SCHEDULE, IV)The INPUT argument can be of arbitrary length, although it will be internally padded on the right with NULs to the nearest multiple of 8 bytes. INPUT is taken and encrypted using CBC mode with key schedule SCHEDULE and initialisation vector IV. If OUTPUT is not undef then it assumed to be an lvalue which is grown (if necessary) and receives the encrypted output. Whether or not OUTPUT is undef, the output is also available as the return value of the function.cbc_decrypt (INPUT, OUTPUT, SCHEDULE, IV)The INPUT argument can be of arbitrary length, although it will be internally padded on the right with NULs to the nearest multiple of 8 bytes. INPUT is taken and decrypted using CBC mode with key schedule SCHEDULE and initialisation vector IV. If OUTPUT is not undef then it assumed to be an lvalue which is grown (if necessary) and receives the decrypted output. Whether or not OUTPUT is undef, the output is also available as the return value of the function.pcbc_encrypt (INPUT, OUTPUT, SCHEDULE, IV)The INPUT argument can be of arbitrary length, although it will be internally padded on the right with NULs to the nearest multiple of 8 bytes. INPUT is taken and encrypted using PCBC mode with key schedule SCHEDULE and initialisation vector IV. If OUTPUT is not undef then it assumed to be an lvalue which is grown (if necessary) and receives the encrypted output. Whether or not OUTPUT is undef, the output is also available as the return value of the function.pcbc_decrypt (INPUT, OUTPUT, SCHEDULE, IV)The INPUT argument can be of arbitrary length, although it will be internally padded on the right with NULs to the nearest multiple of 8 bytes. INPUT is taken and decrypted using PCBC mode with key schedule SCHEDULE and initialisation vector IV. If OUTPUT is not undef then it assumed to be an lvalue which is grown (if necessary) and receives the decrypted output. Whether or not OUTPUT is undef, the output is also available as the return value of the function.pcbc_cksum (INPUT, SCHEDULE, IV)The INPUT argument can be of arbitrary length, although it will be internally padded on the right with NULs to the nearest multiple of 8 bytes. CBC mode is used to generate an 8-byte cryptographic checksum using key schedule SCHEDULE and initialisation vector IV. This checksum is returned.Functions in package Des which can be importedrandom_key ()Produces a random DES key based on current time, PID and a counter.read_password (PROMPT )Prints PROMPT on the terminal, turns off echo if possible and reads a password from the keyboard. If the optional VERIFY argument is present and true than the password is prompted for a second time and the two are compared. If different, the prompting is repeated. The resulting string is turned into a DES key (using string_to_key (q.v.) internally) and that key is returned. Requirements: · Perl

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