| .TH DES 3 |
| .SH NAME |
| setupDESstate, des_key_setup, block_cipher, desCBCencrypt, desCBCdecrypt, desECBencrypt, desECBdecrypt, des3CBCencrypt, des3CBCdecrypt, des3ECBencrypt, des3ECBdecrypt, key_setup, des56to64, des64to56, setupDES3state, triple_block_cipher, - single and triple digital encryption standard |
| .SH SYNOPSIS |
| .B #include <u.h> |
| .br |
| .B #include <libc.h> |
| .br |
| .B #include <mp.h> |
| .br |
| .B #include <libsec.h> |
| .PP |
| .B |
| void des_key_setup(uchar key[8], ulong schedule[32]) |
| .PP |
| .B |
| void block_cipher(ulong *schedule, uchar *data, |
| .B |
| int decrypting) |
| .PP |
| .B |
| void setupDESstate(DESstate *s, uchar key[8], uchar *ivec) |
| .PP |
| .B |
| void desCBCencrypt(uchar*, int, DESstate*) |
| .PP |
| .B |
| void desCBCdecrypt(uchar*, int, DESstate*) |
| .PP |
| .B |
| void desECBencrypt(uchar*, int, DESstate*) |
| .PP |
| .B |
| void desECBdecrypt(uchar*, int, DESstate*) |
| .PP |
| .B |
| void triple_block_cipher(ulong keys[3][32], uchar*, int) |
| .PP |
| .B |
| void setupDES3state(DES3state *s, uchar key[3][8], |
| .B |
| uchar *ivec) |
| .PP |
| .B |
| void des3CBCencrypt(uchar*, int, DES3state*) |
| .PP |
| .B |
| void des3CBCdecrypt(uchar*, int, DES3state*) |
| .PP |
| .B |
| void des3ECBencrypt(uchar*, int, DES3state*) |
| .PP |
| .B |
| void des3ECBdecrypt(uchar*, int, DES3state*) |
| .PP |
| .B |
| void key_setup(uchar[7], ulong[32]) |
| .PP |
| .B |
| void des56to64(uchar *k56, uchar *k64) |
| .PP |
| .B |
| void des64to56(uchar *k64, uchar *k56) |
| .SH DESCRIPTION |
| .PP |
| The Digital Encryption Standard (DES) |
| is a shared key or symmetric encryption using either |
| a 56 bit key for single DES or three 56 bit keys for triple des. |
| The keys are encoded into 64 bits where every eight bit |
| is parity. |
| .PP |
| The basic DES function, |
| .IR block_cipher , |
| works on a block of 8 bytes, converting them in place. |
| It takes a key schedule, a pointer to the block, and |
| a flag indicating encrypting (0) or decrypting (1). |
| The key schedule is created from the key using |
| .IR des_key_setup . |
| .PP |
| Since it is a bit awkward, |
| .I block_cipher |
| is rarely called directly. Instead, one normally uses |
| routines that encrypt larger buffers of data and |
| which may chain the encryption state from one buffer |
| to the next. |
| These routines keep track of the state of the |
| encryption using a |
| .B DESstate |
| structure that contains the key schedule and any chained |
| state. |
| .I SetupDESstate |
| sets up the |
| .B DESstate |
| structure using the key and an 8 byte initialization vector. |
| .PP |
| Electronic code book, using |
| .I desECBencrypt |
| and |
| .IR desECBdecrypt , |
| is the less secure mode. The encryption of each 8 bytes |
| does not depend on the encryption of any other. |
| Hence the encryption is a substitution |
| cipher using 64 bit characters. |
| .PP |
| Cipher block chaining mode, using |
| .I desCBCencrypt |
| and |
| .IR desCBCdecrypt , |
| is more secure. Every block encrypted depends on the initialization |
| vector and all blocks encrypted before it. |
| .PP |
| For both CBC and ECB modes, a stream of data can be encrypted as |
| multiple buffers. However, all buffers except the last must |
| be a multiple of 8 bytes to ensure successful decryption of |
| the stream. |
| .PP |
| There are equivalent triple DES functions for each of the |
| DES functions. |
| .PP |
| In the past Plan 9 used a 56 bit or 7 byte |
| format for DES keys. To be compatible with the rest |
| of the world, we've abandoned this format. |
| There are two functions: |
| .I des56to64 |
| and |
| .I des64to56 |
| to convert back and forth between the two formats. |
| Also a key schedule can be set up from the 7 byte format |
| using |
| .IR key_setup . |
| .PP |
| .SH SOURCE |
| .B \*9/src/libsec |
| .SH SEE ALSO |
| .IR mp (3), |
| .IR aes (3), |
| .IR blowfish (3), |
| .IR dsa (3), |
| .IR elgamal (3), |
| .IR rc4 (3), |
| .IR rsa (3), |
| .IR sechash (3), |
| .IR prime (3), |
| .IR rand (3) |
