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doc: indicate sha1 has the same limitations as md5

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* doc/coreutils.texi (sha1sum invocation): Given that a SHA-1
preimage attack has occurred as documented at http://shattered.io/,
document sha1sum as having the same limitations as md5sum.
(md5sum): Parameterize the warning for use in both cases.
* man/md5sum.x: Mention b2sum(1) as a more secure alternative.
* man/sha1sum.x: Give the same warning as done for md5sum(1).
This commit is contained in:
Pádraig Brady
2017-02-28 20:14:58 -08:00
parent 06c3123f6e
commit 109ba4441b
3 changed files with 15 additions and 11 deletions
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18
doc/coreutils.texi
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@@ -3818,16 +3818,19 @@ as the length is automatically determined when checking.
@command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
@dfn{message-digest}) for each specified @var{file}.
Note: The MD5 digest is more reliable than a simple CRC (provided by
@macro weakHash{hash}
Note: The \hash\ digest is more reliable than a simple CRC (provided by
the @command{cksum} command) for detecting accidental file corruption,
as the chances of accidentally having two files with identical MD5
as the chances of accidentally having two files with identical \hash\
are vanishingly small. However, it should not be considered secure
against malicious tampering: although finding a file with a given MD5
against malicious tampering: although finding a file with a given \hash\
fingerprint is considered infeasible at the moment, it is known how
to modify certain files, including digital certificates, so that they
appear valid when signed with an MD5 digest. For more secure hashes,
appear valid when signed with an \hash\ digest. For more secure hashes,
consider using SHA-2, or the newer @command{b2sum} command.
@xref{sha2 utilities}. @xref{b2sum invocation}.
@end macro
@weakHash{MD5}
If a @var{file} is specified as @samp{-} or if no files are given
@command{md5sum} computes the checksum for the standard input.
@@ -3979,12 +3982,7 @@ exit nonzero after all warnings have been issued.
@var{file}. The usage and options of this command are precisely the
same as for @command{md5sum}. @xref{md5sum invocation}.
Note: The SHA-1 digest is more secure than MD5, and no collisions of
it are known (different files having the same fingerprint). However,
it is known that they can be produced with considerable, but not
unreasonable, resources. For this reason, it is generally considered
that SHA-1 should be gradually phased out in favor of the more secure
SHA-2 hash algorithms. @xref{sha2 utilities}.
@weakHash{SHA-1}
@node sha2 utilities

3
man/md5sum.x
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@@ -5,4 +5,5 @@ md5sum \- compute and check MD5 message digest
[BUGS]
The MD5 algorithm should not be used any more for security related purposes.
Instead, better use an SHA\-2 algorithm, implemented in the programs
sha224sum(1), sha256sum(1), sha384sum(1), sha512sum(1)
sha224sum(1), sha256sum(1), sha384sum(1), sha512sum(1),
or the BLAKE2 algorithm, implemented in b2sum(1)

5
man/sha1sum.x
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@@ -2,3 +2,8 @@
sha1sum \- compute and check SHA1 message digest
[DESCRIPTION]
.\" Add any additional description here
[BUGS]
The SHA-1 algorithm should not be used any more for security related purposes.
Instead, better use an SHA\-2 algorithm, implemented in the programs
sha224sum(1), sha256sum(1), sha384sum(1), sha512sum(1),
or the BLAKE2 algorithm, implemented in b2sum(1)