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59409d0947
I've moved it from mpunsafe.c into the main mpint.c, and renamed it mp_mod_known_integer, because now it manages to avoid leaking information about the mp_int you give it. It can still potentially leak information about the small _modulus_ integer - hence the word 'known' in the new function name. This won't be a problem in any existing use of the function, because it's used during prime generation to check divisibility by all the small primes, and optionally also check for residue 1 mod the RSA public exponent. But all those values are well known and not secret. This removes one source of side-channel leakage from prime generation.
40 lines
1.5 KiB
C
40 lines
1.5 KiB
C
/*
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* mpunsafe.h: functions that deal with mp_ints in ways that are *not*
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* expected to be constant-time. Used during key generation, in which
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* constant run time is a lost cause anyway.
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*
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* These functions are in a separate header, so that you can easily
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* check that you're not calling them in the wrong context. They're
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* also defined in a separate source file, which is only linked in to
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* the key generation tools. Furthermore, that source file also
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* defines a global symbol that intentionally conflicts with one
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* defined in the SSH client code, so that any attempt to put these
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* functions into the same binary as the live SSH client
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* implementation will cause a link-time failure. They should only be
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* linked into PuTTYgen and auxiliary test programs.
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*
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* Also, just in case those precautions aren't enough, all the unsafe
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* functions have 'unsafe' in the name.
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*/
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#ifndef PUTTY_MPINT_UNSAFE_H
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#define PUTTY_MPINT_UNSAFE_H
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/*
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* The most obvious unsafe thing you want to do with an mp_int is to
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* get rid of leading zero words in its representation, so that its
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* nominal size is as close as possible to its true size, and you
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* don't waste any time processing it.
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*
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* mp_unsafe_shrink performs this operation in place, mutating the
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* size field of the mp_int it's given. It returns the same pointer it
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* was given.
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*
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* mp_unsafe_copy leaves the original mp_int alone and makes a new one
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* with the minimal size.
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*/
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mp_int *mp_unsafe_shrink(mp_int *m);
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mp_int *mp_unsafe_copy(mp_int *m);
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#endif /* PUTTY_MPINT_UNSAFE_H */
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