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
24 program generates and verifies cryptographic checksums (hashes) of
25 files. A number of hashing algorithms are available.
29 program's options and output are designed to be upwardly compatible with
36 generates checksums of a collection of files named either on the command
37 line or read from standard input, and write their hashes to standard
38 output using a simple file format. However, given the
40 option, it will read in files in its usual output format and verify that
41 the named files have the reported hashes.
45 program understands the following options:
48 Prints a help message to standard output and exits successfully.
51 Prints the program's version number to standard output and exits
55 Prints a brief usage summary to standard output and exits successfully.
57 .BR "\-l, \-\-list " [ \fIitem ...]
58 Show lists of hash functions and encodings supported.
60 .BI "\-a, \-\-algorithm=" alg
61 Use the hash algorithm
63 If this option is not given, a default hashing algorithm is selected:
65 .B "Hashing algorithms"
68 .BI "\-E, \-\-encoding=" encoding
71 to represent hashes in the output. This is not interoperable with other
72 programs, but it's handy, e.g., for building sha1 URNs. The encodings
80 .B hashsum \-\-list enc
81 for a list of supported encodings.
84 Each input file is considered to be a list of filenames which should be
85 read and hashed. By default, the filenames are considered to be
86 whitespace-separated, although control characters can be escaped (see
87 .B "Escaping control characters"
91 In conjunction with the
93 option above, reads null-terminated filenames, as emitted by GNU
96 option, rather than whitespace-delimited filenames. If the
98 option is also given, each named in the list is a list of filename/hash
102 Escape control characters (see
103 .B "Escaping control characters"
104 below) in filenames when generating output. Escaped
105 output is not compatible with
107 but copes better with files containing newlines and other strange
111 Check hashes. Each input file is assumed to be in
113 output format. It is read, and
115 will verify that each named file has the correct hash. Assuming that
116 the hash list is authentic (e.g., it has been digitally signed, or
117 obtained via some secure medium), this provides strong assurance that
118 the files listed have not been tampered with.
121 Assume that the files to be hashed are binary files. This doesn't make
122 any difference in Unix systems, although it might on other platforms
123 which draw a distinction.
125 .B "\-v, \-\-verbose"
126 In conjunction with the
128 option above, be verbose when checking files.
130 If no filenames are given on the command line, standard input is read.
131 Standard input does not have a filename.
133 There are three types of line in
145 character. Two directives are currently understood:
148 Subsequent hashes in this file were generated using the algorithm
151 .BI "#encoding " encoding
152 Subsequent hashes in this file are represented using the named
156 Filenames in subsequence lines are written using the `escaped' format,
161 consists of a hash, in the requested encoding, followed by a space, a
163 and the filename. The
167 to indicate that the file should be read in binary mode, or a space.
168 The rest of the line contains the filename.
172 line is one which doesn't look like a directive or a file line. Rubbish
173 lines are ignored. Hence, you can apply PGP clear-signing to a
175 file without preventing it from being read.
176 .SS "Escaping control characters"
177 When reading filenames to hash from a list of files or an escaped hash
178 list, the following rules are obeyed:
180 An escaped string cannot contain unescaped, unquoted whitespace
181 characters. If such a character is found, the string is considered to
186 escapes the following character. If the character is one of
195 it is replaced by the control character for an audible alert, backspace,
196 form-feed, newline, carriage return, horizontal tab or vertical tab
197 respectively; other escaped characters are unchanged, although they lose
198 any special meaning they might have had.
200 A section of text may be quoted by surrounding it by
205 pairs. Within a quoted section, whitespace characters may appear
206 unescaped. The backslash may be used to quote control characters or the
207 quoting characters as usual.
209 A word beginning with a hash
211 character is considered to begin a
213 which extends to the end of the current line. The hash character may be
215 .SS "Hashing algorithms"
218 program understands several hashing algorithms:
221 Designed by Ron Rivest, although I don't know when, and described in
222 RFC1319, MD2 is a really old and slow hash function. Its security is
223 suspect too: only its checksum stands between it and collision-finding
224 attacks. Use of MD2 is not recommended, though it's still used in
228 Designed by Ron Rivest in 1990 and 1992 respectively and described in
229 RFCs 1186, 1320 and 1321, these two early hash functions are efficient
230 but cryptographically suspect: the MD4 algorithm has been shown not to
231 be collision-resistant and there are `pseudo-collisions' in MD5.
234 has been used heavily since its introduction and is still popular. MD4
235 is still useful when a fast non-cryptographic hash is wanted.
238 Designed by the US National Security Agency as part of the Digital
239 Signature Standard, SHA-1 provides a longer output than
243 and is seen as being more secure.
245 .BR rmd128 ", " rmd160 ", " rmd256 " and " rmd320
246 Designed by Antoon Bosselaers, Hans Dobbertin and Bart Preneel in 1996
247 as a replacement for the earlier RIPEMD algorithm, RIPEMD160 provides
248 the same length output as SHA-1, but has been designed in the open by
249 experts. RIPEMD28 is a shortened version of RIPEMD160 designed as a
250 drop-in replacement for MD4, MD5 and the old RIPEMD. The 256 and
251 320-bit versions are efficient double-width extensions of the 128 and
252 160-bit hashes, although they may not offer any additional security.
255 Designed by Ross Anderson and Eli Biham to take advantage of 64-bit
256 processors, Tiger seems to be an efficient and strong hash function.
257 It's a relatively new algorithm, however, and should probably be
258 approached with an open-minded caution.
260 .BR sha256 ", " sha384 " and " sha512
261 Designed by the US National Security Agency to provide security
262 commensurate with the Advanced Encryption Standard, these hash functions
263 provide long outputs. SHA-256 is fairly quick, though the longer
264 variants are slower on 32-bit hardware since they require 64-bit
265 arithmetic. They're all very new at the moment, and should be
266 approached with an open-minded caution.
268 The default hashing algorithm is determined by looking at the name by
269 which it was invoked passed to it in
276 is the name of a hash function, that hash becomes the default. (Hence,
278 can be used as a drop-in replacement for
280 If the program name doesn't match an algorithm, then
282 is selected for compatibility with files generated by
285 Note that the same default algorithm is used for both generating new
286 output files and checking existing ones. If the algorithm is forced by
293 directive in its output.
300 Mark Wooding, <mdw@distorted.org.uk>
projects / u / mdw / catacomb / blob