String-Compare-ConstantTime-0.312/0000755000175000017500000000000013050633220015427 5ustar dougdougString-Compare-ConstantTime-0.312/lib/0000755000175000017500000000000013050633220016175 5ustar dougdougString-Compare-ConstantTime-0.312/lib/String/0000755000175000017500000000000013050633220017443 5ustar dougdougString-Compare-ConstantTime-0.312/lib/String/Compare/0000755000175000017500000000000013050633220021031 5ustar dougdougString-Compare-ConstantTime-0.312/lib/String/Compare/ConstantTime.pm0000644000175000017500000001376513050633066024023 0ustar dougdougpackage String::Compare::ConstantTime; use strict; our $VERSION = '0.312'; require XSLoader; XSLoader::load('String::Compare::ConstantTime', $VERSION); require Exporter; use base 'Exporter'; our @EXPORT_OK = qw(equals); ## equals is defined in ConstantTime.xs 1; __END__ =encoding utf-8 =head1 NAME String::Compare::ConstantTime - Timing side-channel protected string compare =head1 SYNOPSIS use String::Compare::ConstantTime; if (String::Compare::ConstantTime::equals($secret_data, $user_supplied_data)) { ## The strings are eq } An example with HMACs: use String::Compare::ConstantTime; use Digest::HMAC_SHA1; ## or whatever my $hmac_ctx = Digest::HMAC_SHA1->new($key); $hmac_ctx->add($data); my $digest = $hmac_ctx->digest; if (String::Compare::ConstantTime::equals($digest, $candidate_digest)) { ## The candidate digest is valid } =head1 DESCRIPTION This module provides one function, C (not exported by default). You should pass this function two strings of the same length. Just like perl's C, it will return true if they are string-wise identical and false otherwise. However, comparing any two differing strings of the same length will take a fixed amount of time. If the lengths of the strings are different, C will return false right away. =head1 TIMING SIDE-CHANNEL Some programs take different amounts of time to run depending on the input values provided to them. Untrusted parties can sometimes learn information you might not want them to know by measuring this time. This is called a "timing side-channel". Most routines that compare strings (like perl's C and C and C's C and C) start scanning from the start of the strings and terminate as soon as they determine the strings won't match. This is good for efficiency but bad because it opens a timing side-channel. If one of the strings being compared is a secret and the other is controlled by some untrusted party, it is sometimes possible for this untrusted party to learn the secret using a timing side-channel. If the lengths of the strings are different, because C returns false right away the size of the secret string may be leaked (but not its contents). =head1 HMAC HMACs are "Message Authentication Codes" built on top of cryptographic hashes. The HMAC algorithm produces digests that are included along with a message in order to verify that whoever created the message knows a particular secret password, and that this message hasn't been tampered with since. To verify a candidate digest included with a message, you re-compute the digest using the message and the secret password. If this computed digest is is the same as the candidate digest then the message is considered authenticated. A common side-channel attack against services that verify unlimited numbers of messages automatically is to create a forged message and then just send some random junk as the candidate digest. Continue sending this message and junk digests that vary by the first character. Repeat many times. If you find a particular digest that statistically takes a longer time to be rejected than the other digests, it is probably because this particular digest has the first character correct and the service's final string comparison is running slightly longer. At this point, you keep this first character fixed and start varying the second character until it is solved. Repeat until all the characters are solved or until the amount of remaining possibilities are so small you can brute force it. At this point, your candidate digest is considered valid and you have forged a message. Note that this particular attack doesn't allow the attacker to recover the secret input key to the HMAC but nevertheless can produce a valid digest for any message given enough time because the service that validates the HMAC is acting as an "oracle". B: Although this module protects against a common attack against applications that store state in browser cookies, it is in no way an endorsement of this practise. =head1 LOCK-PICKING ANALOGY Pin tumbler locks are susceptible to being picked in a similar way to an attacker forging HMAC digests using a timing side-channel. The traditional way to pick cheap pin tumbler locks is to apply torque to the lock cylinder so that the pins are pressed against the cylinder. However, because of slight manufacturing discrepancies one particular pin will be the widest by a slight margin and will be pressed against the cylinder tighter than the others (the cheaper the lock, the higher the manufacturing tolerances). The attacker lifts this pin until the cylinder gives a little bit, indicating that this pin has been solved and the next widest pin is now the one being pressed against the cylinder the tighest. This process is repeated until all the pins are solved and the lock opens. Just like an attacker trying to solve HMAC digests can work on one character at a time, a lock pick can work on each pin in isolation. To protect against this, quality locks force all pins to be fixed into place before the cylinder rotation can be attempted, just as secure HMAC verifiers force attackers to guess the entire digest on each attempt. =head1 SEE ALSO L L has a good section on side-channel cryptanalysis such as it pertains to password storage (mostly, it doesn't). L L L L L =head1 AUTHOR Doug Hoyte, C<< >> =head1 COPYRIGHT & LICENSE Copyright 2012-2017 Doug Hoyte. This module is licensed under the same terms as perl itself. =cut String-Compare-ConstantTime-0.312/ConstantTime.xs0000644000175000017500000000172713050632743020433 0ustar dougdoug#include "EXTERN.h" #include "perl.h" #include "XSUB.h" static int do_compare(unsigned char *a, unsigned char *b, size_t n) { size_t i; unsigned char r = 0; for (i = 0; i < n; i++) { r |= *a++ ^ *b++; } return r; } MODULE = String::Compare::ConstantTime PACKAGE = String::Compare::ConstantTime PROTOTYPES: ENABLE int equals(a, b) SV *a SV *b CODE: size_t alen; unsigned char *ap; size_t blen; unsigned char *bp; int r; SvGETMAGIC(a); SvGETMAGIC(b); if (SvOK(a) && SvOK(b)) { alen = SvCUR(a); ap = SvPV(a, alen); blen = SvCUR(b); bp = SvPV(b, blen); if (alen == blen) { r = !do_compare(ap, bp, alen); } else { r = 0; } } else if (SvOK(a) || SvOK(b)) { r = 0; } else { r = 1; } RETVAL = r; OUTPUT: RETVAL String-Compare-ConstantTime-0.312/META.yml0000664000175000017500000000123313050633220016701 0ustar dougdoug--- abstract: unknown author: - unknown build_requires: ExtUtils::MakeMaker: '0' configure_requires: ExtUtils::MakeMaker: '0' dynamic_config: 1 generated_by: 'ExtUtils::MakeMaker version 7.0401, CPAN::Meta::Converter version 2.150005' license: perl meta-spec: url: http://module-build.sourceforge.net/META-spec-v1.4.html version: '1.4' name: String-Compare-ConstantTime no_index: directory: - t - inc requires: {} resources: bugtracker: https://github.com/hoytech/String-Compare-ConstantTime/issues repository: git://github.com/hoytech/String-Compare-ConstantTime.git version: '0.312' x_serialization_backend: 'CPAN::Meta::YAML version 0.018' String-Compare-ConstantTime-0.312/COPYING0000644000175000017500000000007513050632443016472 0ustar dougdougThis module is licensed under the same terms as perl itself. String-Compare-ConstantTime-0.312/t/0000755000175000017500000000000013050633220015672 5ustar dougdougString-Compare-ConstantTime-0.312/t/accuracy.t0000644000175000017500000000136513050632443017664 0ustar dougdouguse String::Compare::ConstantTime qw/equals/; use strict; use utf8; use Test::More tests => 18; ok(equals("asdf", "asdf")); ok(!equals("asdf", "asdg")); ok(!equals("asdf", "asdfg")); ok(!equals("asdfg", "asdf")); ok(equals("a"x1000, "a"x1000)); ok(!equals("a"x1000, "a"x999 . "b")); ok(!equals("a"x400 . "b" . "a"x599, "a"x1000)); ok(equals("\x00"x65, "\x00"x65)); ok(!equals("\x00"x65, "\x00"x64)); ok(equals(1, 1)); ok(equals(10000000, 10000000)); ok(!equals(10000000, 10000070)); ok(equals("λ", "λ")); ok(equals("λλλλλλλ", "λλλλλλλ")); ok(equals(join("", ( map { chr } (0 .. 255) )) x 10, join("", ( map { chr } (0 .. 255) )) x 10)); ok(!equals("asdf", undef)); ok(!equals(undef, "asdf")); ok(equals(undef, undef)); String-Compare-ConstantTime-0.312/t/stats.t0000644000175000017500000000024513050632443017224 0ustar dougdouguse String::Compare::ConstantTime; use strict; use Test::More skip_all => q{Need to figure out a way to portable collect granular timing data -- see git history}; String-Compare-ConstantTime-0.312/t/magic.t0000644000175000017500000000025613050632743017153 0ustar dougdouguse String::Compare::ConstantTime qw/equals/; use strict; use Test::More tests => 2; ok equals substr( "asdfg", 0, 4 ), "asdf"; ok equals "asdf", substr( "asdfg", 0, 4 ); String-Compare-ConstantTime-0.312/README0000664000175000017500000001374113050633220016317 0ustar dougdougNAME String::Compare::ConstantTime - Timing side-channel protected string compare SYNOPSIS use String::Compare::ConstantTime; if (String::Compare::ConstantTime::equals($secret_data, $user_supplied_data)) { ## The strings are eq } An example with HMACs: use String::Compare::ConstantTime; use Digest::HMAC_SHA1; ## or whatever my $hmac_ctx = Digest::HMAC_SHA1->new($key); $hmac_ctx->add($data); my $digest = $hmac_ctx->digest; if (String::Compare::ConstantTime::equals($digest, $candidate_digest)) { ## The candidate digest is valid } DESCRIPTION This module provides one function, "equals" (not exported by default). You should pass this function two strings of the same length. Just like perl's "eq", it will return true if they are string-wise identical and false otherwise. However, comparing any two differing strings of the same length will take a fixed amount of time. If the lengths of the strings are different, "equals" will return false right away. TIMING SIDE-CHANNEL Some programs take different amounts of time to run depending on the input values provided to them. Untrusted parties can sometimes learn information you might not want them to know by measuring this time. This is called a "timing side-channel". Most routines that compare strings (like perl's "eq" and "cmp" and C's "strcmp" and "memcmp") start scanning from the start of the strings and terminate as soon as they determine the strings won't match. This is good for efficiency but bad because it opens a timing side-channel. If one of the strings being compared is a secret and the other is controlled by some untrusted party, it is sometimes possible for this untrusted party to learn the secret using a timing side-channel. If the lengths of the strings are different, because "equals" returns false right away the size of the secret string may be leaked (but not its contents). HMAC HMACs are "Message Authentication Codes" built on top of cryptographic hashes. The HMAC algorithm produces digests that are included along with a message in order to verify that whoever created the message knows a particular secret password, and that this message hasn't been tampered with since. To verify a candidate digest included with a message, you re-compute the digest using the message and the secret password. If this computed digest is is the same as the candidate digest then the message is considered authenticated. A common side-channel attack against services that verify unlimited numbers of messages automatically is to create a forged message and then just send some random junk as the candidate digest. Continue sending this message and junk digests that vary by the first character. Repeat many times. If you find a particular digest that statistically takes a longer time to be rejected than the other digests, it is probably because this particular digest has the first character correct and the service's final string comparison is running slightly longer. At this point, you keep this first character fixed and start varying the second character until it is solved. Repeat until all the characters are solved or until the amount of remaining possibilities are so small you can brute force it. At this point, your candidate digest is considered valid and you have forged a message. Note that this particular attack doesn't allow the attacker to recover the secret input key to the HMAC but nevertheless can produce a valid digest for any message given enough time because the service that validates the HMAC is acting as an "oracle". NOTE: Although this module protects against a common attack against applications that store state in browser cookies, it is in no way an endorsement of this practise. LOCK-PICKING ANALOGY Pin tumbler locks are susceptible to being picked in a similar way to an attacker forging HMAC digests using a timing side-channel. The traditional way to pick cheap pin tumbler locks is to apply torque to the lock cylinder so that the pins are pressed against the cylinder. However, because of slight manufacturing discrepancies one particular pin will be the widest by a slight margin and will be pressed against the cylinder tighter than the others (the cheaper the lock, the higher the manufacturing tolerances). The attacker lifts this pin until the cylinder gives a little bit, indicating that this pin has been solved and the next widest pin is now the one being pressed against the cylinder the tighest. This process is repeated until all the pins are solved and the lock opens. Just like an attacker trying to solve HMAC digests can work on one character at a time, a lock pick can work on each pin in isolation. To protect against this, quality locks force all pins to be fixed into place before the cylinder rotation can be attempted, just as secure HMAC verifiers force attackers to guess the entire digest on each attempt. SEE ALSO The String-Compare-ConstantTime github repo Authen::Passphrase has a good section on side-channel cryptanalysis such as it pertains to password storage (mostly, it doesn't). The famous TENEX password bug Example of a timing bug QSCAN Practical limits of the timing side channel NaCl: Crypto library designed to prevent side channel attacks AUTHOR Doug Hoyte, "" COPYRIGHT & LICENSE Copyright 2012-2017 Doug Hoyte. This module is licensed under the same terms as perl itself. String-Compare-ConstantTime-0.312/MANIFEST0000644000175000017500000000051313050633220016557 0ustar dougdougChanges ConstantTime.xs COPYING lib/String/Compare/ConstantTime.pm Makefile.PL MANIFEST This list of files MANIFEST.SKIP README t/accuracy.t t/magic.t t/stats.t META.yml Module YAML meta-data (added by MakeMaker) META.json Module JSON meta-data (added by MakeMaker) String-Compare-ConstantTime-0.312/Makefile.PL0000644000175000017500000000147313050632443017414 0ustar dougdouguse strict; use ExtUtils::MakeMaker; my %args = ( NAME => 'String::Compare::ConstantTime', VERSION_FROM => 'lib/String/Compare/ConstantTime.pm', PREREQ_PM => { }, LIBS => [''], DEFINE => '', INC => '-I.', OBJECT => 'ConstantTime.o', LICENSE => 'perl', dist => { PREOP => 'pod2text $(VERSION_FROM) > $(DISTVNAME)/README', }, ); my $eummv = eval ($ExtUtils::MakeMaker::VERSION); if ($eummv >= 6.45) { $args{META_MERGE} = { resources => { repository => 'git://github.com/hoytech/String-Compare-ConstantTime.git', bugtracker => 'https://github.com/hoytech/String-Compare-ConstantTime/issues', }, }; } WriteMakefile(%args); String-Compare-ConstantTime-0.312/MANIFEST.SKIP0000644000175000017500000000025513050632443017335 0ustar dougdougMANIFEST.bak Makefile.old Makefile$ README.pod .gitignore .git/ blib/ pm_to_blib ConstantTime.o ConstantTime.c ConstantTime.bs String-Compare-ConstantTime-*.tar.gz MYMETA.* String-Compare-ConstantTime-0.312/META.json0000664000175000017500000000212713050633220017054 0ustar dougdoug{ "abstract" : "unknown", "author" : [ "unknown" ], "dynamic_config" : 1, "generated_by" : "ExtUtils::MakeMaker version 7.0401, CPAN::Meta::Converter version 2.150005", "license" : [ "perl_5" ], "meta-spec" : { "url" : "http://search.cpan.org/perldoc?CPAN::Meta::Spec", "version" : "2" }, "name" : "String-Compare-ConstantTime", "no_index" : { "directory" : [ "t", "inc" ] }, "prereqs" : { "build" : { "requires" : { "ExtUtils::MakeMaker" : "0" } }, "configure" : { "requires" : { "ExtUtils::MakeMaker" : "0" } }, "runtime" : { "requires" : {} } }, "release_status" : "stable", "resources" : { "bugtracker" : { "web" : "https://github.com/hoytech/String-Compare-ConstantTime/issues" }, "repository" : { "url" : "git://github.com/hoytech/String-Compare-ConstantTime.git" } }, "version" : "0.312", "x_serialization_backend" : "JSON::PP version 2.27300" } String-Compare-ConstantTime-0.312/Changes0000644000175000017500000000100613050633051016721 0ustar dougdoug0.312 2017-02-14 * Now works with variables that have magic such as results of substr, tied variables, etc. (thanks James Raspass) 0.311 2015-10-24 * Don't ship MYMETA files anymore (thanks Adel Qalieh and Alexandr Ciornii) 0.310 2014-09-23 * Fix segfault when passed in undef (thanks Ichinose Shogo) * Documentation updates * Add github repo and license meta info 0.300 2012-10-09 * Change version number format * Skip unreliable stats test for now 0.20 2012-07-12 * Initial release