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.TH ENCRYPT 2
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.SH NAME
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encrypt, decrypt, netcrypt \- DES encryption
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.SH SYNOPSIS
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.B #include <u.h>
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.br
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.B #include <libc.h>
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.PP
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.B
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int	encrypt(void *key, void *data, int len)
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.PP
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.B
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int	decrypt(void *key, void *data, int len)
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.PP
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.B
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int	netcrypt(void *key, void *data)
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.SH DESCRIPTION
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.I Encrypt
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and
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.I decrypt
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perform DES encryption and decryption.
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.I Key
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is an array of
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.B DESKEYLEN
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(defined as 7 in
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.BR <auth.h> )
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bytes containing the encryption key.
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.I Data
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is an array of
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.I len
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bytes;
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it must be at least 8 bytes long.
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The bytes are encrypted or decrypted in place.
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.PP
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The DES algorithm encrypts an individual 8-byte block of data.
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.I Encrypt
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uses the following method to encrypt data longer than 8 bytes.
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The first 8 bytes are encrypted as usual.
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The last byte of the encrypted result
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is prefixed to the next 7 unencrypted bytes to make the next 8
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bytes to encrypt.
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This is repeated until fewer than 7 bytes remain unencrypted.
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Any remaining unencrypted bytes are encrypted with enough of the preceding
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encrypted bytes to make a full 8-byte block.
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.I Decrypt
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uses the inverse algorithm.
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.PP
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.I Netcrypt
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performs the same encryption as a SecureNet Key.
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.I Data
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points to an
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.SM ASCII
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string of decimal digits with numeric value between 0 and 10000.
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These digits are copied into an 8-byte buffer with trailing binary zero fill
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and encrypted as one DES block.
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The first four bytes are each formatted as two digit
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.SM ASCII
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hexadecimal numbers,
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and the string is copied into
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.IR data .
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.SH SOURCE
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.B /sys/src/libc/port
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.SH DIAGNOSTICS
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These routines return 1 if the data was encrypted,
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and 0 if the encryption fails.
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.I Encrypt
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and
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.I decrypt
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fail if the data passed is less than 8 bytes long.
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.I Netcrypt
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can fail if it is passed invalid data.
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.SH SEE ALSO
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.IR securenet (8)
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.SH BUGS
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The implementation is broken in a way that makes
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it unsuitable for anything but authentication.