5 \h'-\w'\\$1\ 'u'\\$1\ \c
10 .TH hashsum 1 "29 July 2000" "Straylight/Edgeware" "Catacomb cryptographic library"
12 hashsum \- compute and verify cryptographic checksums of files
22 program generates and verifies cryptographic checksums (hashes) of
23 files. A number of hashing algorithms are available.
27 program's options and output are designed to be upwardly compatible with
34 generates checksums of a collection of files named either on the command
35 line or read from standard input, and write their hashes to standard
36 output using a simple file format. However, given the
38 option, it will read in files in its usual output format and verify that
39 the named files have the reported hashes.
43 program understands the following options:
46 Prints a help message to standard output and exits successfully.
49 Prints the program's version number to standard output and exits
53 Prints a brief usage summary to standard output and exits successfully.
55 .BI "\-a, \-\-algorithm=" alg
56 Use the hash algorithm
58 If this option is not given, a default hashing algorithm is selected:
60 .B "Hashing algorithms"
64 Prints a space-separated list of available hashing algorithms to
65 standard output and exits successfully.
68 Each input file is considered to be a list of filenames which should be
69 read and hashed. By default, the filenames are considered to be
70 whitespace-separated, although control characters can be escaped (see
71 .B "Escaping control characters"
75 In conjunction with the
77 option above, reads null-terminated filenames, as emitted by GNU
80 option, rather than whitespace-delimited filenames. If the
82 option is also given, each named in the list is a list of filename/hash
86 Escape control characters (see
87 .B "Escaping control characters"
88 below) in filenames when generating output. Escaped
89 output is not compatible with
91 but copes better with files containing newlines and other strange
95 Check hashes. Each input file is assumed to be in
97 output format. It is read, and
99 will verify that each named file has the correct hash. Assuming that
100 the hash list is authentic (e.g., it has been digitally signed, or
101 obtained via some secure medium), this provides strong assurance that
102 the files listed have not been tampered with.
105 Assume that the files to be hashed are binary files. This doesn't make
106 any difference in Unix systems, although it might on other platforms
107 which draw a distinction.
109 .B "\-v, \-\-verbose"
110 In conjunction with the
112 option above, be verbose when checking files.
114 If no filenames are given on the command line, standard input is read.
115 Standard input does not have a filename.
117 There are three types of line in
129 character. Two directives are currently understood:
132 Subsequent hashes in this file were generated using the algorithm
136 Filenames in subsequence lines are written using the `escaped' format,
141 consists of a hash, in hexadecimal, followed by a space, a
143 and the filename. If the current hash algorithm produces
145 output, there must be
147 hex digits of hash in a file line. The
151 to indicate that the file should be read in binary mode, or a space.
152 The rest of the line contains the filename.
156 line is one which doesn't look like a directive or a file line. Rubbish
157 lines are ignored. Hence, you can apply PGP clear-signing to a
159 file without preventing it from being read.
160 .SS "Escaping control characters"
161 When reading filenames to hash from a list of files or an escaped hash
162 list, the following rules are obeyed:
164 An escaped string cannot contain unescaped, unquoted whitespace
165 characters. If such a character is found, the string is considered to
170 escapes the following character. If the character is one of
179 it is replaced by the control character for an audible alert, backspace,
180 form-feed, newline, carriage return, horizontal tab or vertical tab
181 respectively; other escaped characters are unchanged, although they lose
182 any special meaning they might have had.
184 A section of text may be quoted by surrounding it by
189 pairs. Within a quoted section, whitespace characters may appear
190 unescaped. The backslash may be used to quote control characters or the
191 quoting characters as usual.
193 A word beginning with a hash
195 character is considered to begin a
197 which extends to the end of the current line. The hash character may be
199 .SS "Hashing algorithms"
202 program understands several hashing algorithms:
205 Designed by Ron Rivest, although I don't know when, and described in
206 RFC1319, MD2 is a really old and slow hash function. Its security is
207 suspect too: only its checksum stands between it and collision-finding
208 attacks. Use of MD2 is not recommended, though it's still used in
212 Designed by Ron Rivest in 1990 and 1992 respectively and described in
213 RFCs 1186, 1320 and 1321, these two early hash functions are efficient
214 but cryptographically suspect: the MD4 algorithm has been shown not to
215 be collision-resistant and there are `pseudo-collisions' in MD5.
218 has been used heavily since its introduction and is still popular. MD4
219 is still useful when a fast non-cryptographic hash is wanted.
222 Designed by the US National Security Agency as part of the Digital
223 Signature Standard, SHA-1 provides a longer output than
227 and is seen as being more secure.
229 .BR rmd128 ", " rmd160 ", " rmd256 " and " rmd320
230 Designed by Antoon Bosselaers, Hans Dobbertin and Bart Preneel in 1996
231 as a replacement for the earlier RIPEMD algorithm, RIPEMD160 provides
232 the same length output as SHA-1, but has been designed in the open by
233 experts. RIPEMD28 is a shortened version of RIPEMD160 designed as a
234 drop-in replacement for MD4, MD5 and the old RIPEMD. The 256 and
235 320-bit versions are efficient double-width extensions of the 128 and
236 160-bit hashes, although they may not offer any additional security.
239 Designed by Ross Anderson and Eli Biham to take advantage of 64-bit
240 processors, Tiger seems to be an efficient and strong hash function.
241 It's a relatively new algorithm, however, and should probably be
242 approached with an open-minded caution.
244 .BR sha256 ", " sha384 " and " sha512
245 Designed by the US National Security Agency to provide security
246 commensurate with the Advanced Encryption Standard, these hash functions
247 provide long outputs. SHA-256 is fairly quick, though the longer
248 variants are slower on 32-bit hardware since they require 64-bit
249 arithmetic. They're all very new at the moment, and should be
250 approached with an open-minded caution.
252 The default hashing algorithm is determined by looking at the name by
253 which it was invoked passed to it in
260 is the name of a hash function, that hash becomes the default. (Hence,
262 can be used as a drop-in replacement for
264 If the program name doesn't match an algorithm, then
266 is selected for compatibility with files generated by
269 Note that the same default algorithm is used for both generating new
270 output files and checking existing ones. If the algorithm is forced by
277 directive in its output.
281 Mark Wooding, <mdw@nsict.org>
projects / u / mdw / catacomb / blob