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putty-source/mpint_i.h
Simon Tatham dec79cf152 Start a file of 'unsafe' mp_int functions. 
Unlike the ones in mpint.c proper, these are not intended to respect
the constant-time guarantees. They're going to be the kind of thing
you use in key generation, which is too random to be constant-time in
any case.

I've arranged several precautions to try to make sure these functions
don't accidentally get linked into the main SSH application, only into
key generators:

 - declare them in a separate header with "unsafe" in the name

 - put "unsafe" in the name of every actual function

 - don't even link the mpunsafe.c translation unit into PuTTY proper

 - in fact, define global symbols of the same name in that file and
   the SSH client code, so that there will be a link failure if we
   ever try to do it by accident

The initial contents of the new source file consist of the subroutine
mp_mod_short() that previously lived in sshprime.c (and was not in
mpint.c proper precisely because it was unsafe). While I'm here, I've
turned it into mp_unsafe_mod_integer() and let it take a modulus of up
to 32 bits instead of 16.

Also added some obviously useful functions to shrink an mpint to the
smallest physical size that can hold the contained number (rather like
bn_restore_invariant in the old Bignum system), which I expect to be
using shortly.
2020-02-23 14:49:54 +00:00

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/*
* mpint_i.h: definitions used internally by the bignum code, and
* also a few other vaguely-bignum-like places.
*/
/* ----------------------------------------------------------------------
* The assorted conditional definitions of BignumInt and multiply
* macros used throughout the bignum code to treat numbers as arrays
* of the most conveniently sized word for the target machine.
* Exported so that other code (e.g. poly1305) can use it too.
*
* This code must export, in whatever ifdef branch it ends up in:
*
* - two types: 'BignumInt' and 'BignumCarry'. BignumInt is an
* unsigned integer type which will be used as the base word size
* for all bignum operations. BignumCarry is an unsigned integer
* type used to hold the carry flag taken as input and output by
* the BignumADC macro (see below).
*
* - five constant macros:
* + BIGNUM_INT_BITS, the number of bits in BignumInt,
* + BIGNUM_INT_BYTES, the number of bytes that works out to
* + BIGNUM_TOP_BIT, the BignumInt value consisting of only the top bit
* + BIGNUM_INT_MASK, the BignumInt value with all bits set
* + BIGNUM_INT_BITS_BITS, log to the base 2 of BIGNUM_INT_BITS.
*
* - four statement macros: BignumADC, BignumMUL, BignumMULADD,
* BignumMULADD2. These do various kinds of multi-word arithmetic,
* and all produce two output values.
* * BignumADC(ret,retc,a,b,c) takes input BignumInt values a,b
* and a BignumCarry c, and outputs a BignumInt ret = a+b+c and
* a BignumCarry retc which is the carry off the top of that
* addition.
* * BignumMUL(rh,rl,a,b) returns the two halves of the
* double-width product a*b.
* * BignumMULADD(rh,rl,a,b,addend) returns the two halves of the
* double-width value a*b + addend.
* * BignumMULADD2(rh,rl,a,b,addend1,addend2) returns the two
* halves of the double-width value a*b + addend1 + addend2.
*
* Every branch of the main ifdef below defines the type BignumInt and
* the value BIGNUM_INT_BITS_BITS. The other constant macros are
* filled in by common code further down.
*
* Most branches also define a macro DEFINE_BIGNUMDBLINT containing a
* typedef statement which declares a type _twice_ the length of a
* BignumInt. This causes the common code further down to produce a
* default implementation of the four statement macros in terms of
* that double-width type, and also to defined BignumCarry to be
* BignumInt.
*
* However, if a particular compile target does not have a type twice
* the length of the BignumInt you want to use but it does provide
* some alternative means of doing add-with-carry and double-word
* multiply, then the ifdef branch in question can just define
* BignumCarry and the four statement macros itself, and that's fine
* too.
*/
/* You can lower the BignumInt size by defining BIGNUM_OVERRIDE on the
* command line to be your chosen max value of BIGNUM_INT_BITS_BITS */
#if defined BIGNUM_OVERRIDE
#define BB_OK(b) ((b) <= BIGNUM_OVERRIDE)
#else
#define BB_OK(b) (1)
#endif
#if defined __SIZEOF_INT128__ && BB_OK(6)
/*
* 64-bit BignumInt using gcc/clang style 128-bit BignumDblInt.
*
* gcc and clang both provide a __uint128_t type on 64-bit targets
* (and, when they do, indicate its presence by the above macro),
* using the same 'two machine registers' kind of code generation
* that 32-bit targets use for 64-bit ints.
*/
typedef unsigned long long BignumInt;
#define BIGNUM_INT_BITS_BITS 6
#define DEFINE_BIGNUMDBLINT typedef __uint128_t BignumDblInt
#elif defined _MSC_VER && defined _M_AMD64 && BB_OK(6)
/*
* 64-bit BignumInt, using Visual Studio x86-64 compiler intrinsics.
*
* 64-bit Visual Studio doesn't provide very much in the way of help
* here: there's no int128 type, and also no inline assembler giving
* us direct access to the x86-64 MUL or ADC instructions. However,
* there are compiler intrinsics giving us that access, so we can
* use those - though it turns out we have to be a little careful,
* since they seem to generate wrong code if their pointer-typed
* output parameters alias their inputs. Hence all the internal temp
* variables inside the macros.
*/
#include <intrin.h>
typedef unsigned char BignumCarry; /* the type _addcarry_u64 likes to use */
typedef unsigned __int64 BignumInt;
#define BIGNUM_INT_BITS_BITS 6
#define BignumADC(ret, retc, a, b, c) do \
{ \
BignumInt ADC_tmp; \
(retc) = _addcarry_u64(c, a, b, &ADC_tmp); \
(ret) = ADC_tmp; \
} while (0)
#define BignumMUL(rh, rl, a, b) do \
{ \
BignumInt MULADD_hi; \
(rl) = _umul128(a, b, &MULADD_hi); \
(rh) = MULADD_hi; \
} while (0)
#define BignumMULADD(rh, rl, a, b, addend) do \
{ \
BignumInt MULADD_lo, MULADD_hi; \
MULADD_lo = _umul128(a, b, &MULADD_hi); \
MULADD_hi += _addcarry_u64(0, MULADD_lo, (addend), &(rl)); \
(rh) = MULADD_hi; \
} while (0)
#define BignumMULADD2(rh, rl, a, b, addend1, addend2) do \
{ \
BignumInt MULADD_lo1, MULADD_lo2, MULADD_hi; \
MULADD_lo1 = _umul128(a, b, &MULADD_hi); \
MULADD_hi += _addcarry_u64(0, MULADD_lo1, (addend1), &MULADD_lo2); \
MULADD_hi += _addcarry_u64(0, MULADD_lo2, (addend2), &(rl)); \
(rh) = MULADD_hi; \
} while (0)
#elif (defined __GNUC__ || defined _LLP64 || __STDC__ >= 199901L) && BB_OK(5)
/* 32-bit BignumInt, using C99 unsigned long long as BignumDblInt */
typedef unsigned int BignumInt;
#define BIGNUM_INT_BITS_BITS 5
#define DEFINE_BIGNUMDBLINT typedef unsigned long long BignumDblInt
#elif defined _MSC_VER && BB_OK(5)
/* 32-bit BignumInt, using Visual Studio __int64 as BignumDblInt */
typedef unsigned int BignumInt;
#define BIGNUM_INT_BITS_BITS 5
#define DEFINE_BIGNUMDBLINT typedef unsigned __int64 BignumDblInt
#elif defined _LP64 && BB_OK(5)
/*
* 32-bit BignumInt, using unsigned long itself as BignumDblInt.
*
* Only for platforms where long is 64 bits, of course.
*/
typedef unsigned int BignumInt;
#define BIGNUM_INT_BITS_BITS 5
#define DEFINE_BIGNUMDBLINT typedef unsigned long BignumDblInt
#elif BB_OK(4)
/*
* 16-bit BignumInt, using unsigned long as BignumDblInt.
*
* This is the final fallback for real emergencies: C89 guarantees
* unsigned short/long to be at least the required sizes, so this
* should work on any C implementation at all. But it'll be
* noticeably slow, so if you find yourself in this case you
* probably want to move heaven and earth to find an alternative!
*/
typedef unsigned short BignumInt;
#define BIGNUM_INT_BITS_BITS 4
#define DEFINE_BIGNUMDBLINT typedef unsigned long BignumDblInt
#else
/* Should only get here if BB_OK(4) evaluated false, i.e. the
* command line defined BIGNUM_OVERRIDE to an absurdly small
* value. */
#error Must define BIGNUM_OVERRIDE to at least 4
#endif
#undef BB_OK
/*
* Common code across all branches of that ifdef: define all the
* easy constant macros in terms of BIGNUM_INT_BITS_BITS.
*/
#define BIGNUM_INT_BITS (1 << BIGNUM_INT_BITS_BITS)
#define BIGNUM_INT_BYTES (BIGNUM_INT_BITS / 8)
#define BIGNUM_TOP_BIT (((BignumInt)1) << (BIGNUM_INT_BITS-1))
#define BIGNUM_INT_MASK (BIGNUM_TOP_BIT | (BIGNUM_TOP_BIT-1))
/*
* Just occasionally, we might need a GET_nnBIT_xSB_FIRST macro to
* operate on whatever BignumInt is.
*/
#if BIGNUM_INT_BITS_BITS == 4
#define GET_BIGNUMINT_MSB_FIRST GET_16BIT_MSB_FIRST
#define GET_BIGNUMINT_LSB_FIRST GET_16BIT_LSB_FIRST
#define PUT_BIGNUMINT_MSB_FIRST PUT_16BIT_MSB_FIRST
#define PUT_BIGNUMINT_LSB_FIRST PUT_16BIT_LSB_FIRST
#elif BIGNUM_INT_BITS_BITS == 5
#define GET_BIGNUMINT_MSB_FIRST GET_32BIT_MSB_FIRST
#define GET_BIGNUMINT_LSB_FIRST GET_32BIT_LSB_FIRST
#define PUT_BIGNUMINT_MSB_FIRST PUT_32BIT_MSB_FIRST
#define PUT_BIGNUMINT_LSB_FIRST PUT_32BIT_LSB_FIRST
#elif BIGNUM_INT_BITS_BITS == 6
#define GET_BIGNUMINT_MSB_FIRST GET_64BIT_MSB_FIRST
#define GET_BIGNUMINT_LSB_FIRST GET_64BIT_LSB_FIRST
#define PUT_BIGNUMINT_MSB_FIRST PUT_64BIT_MSB_FIRST
#define PUT_BIGNUMINT_LSB_FIRST PUT_64BIT_LSB_FIRST
#else
#error Ran out of options for GET_BIGNUMINT_xSB_FIRST
#endif
/*
* Common code across _most_ branches of the ifdef: define a set of
* statement macros in terms of the BignumDblInt type provided. In
* this case, we also define BignumCarry to be the same thing as
* BignumInt, for simplicity.
*/
#ifdef DEFINE_BIGNUMDBLINT
typedef BignumInt BignumCarry;
#define BignumADC(ret, retc, a, b, c) do \
{ \
DEFINE_BIGNUMDBLINT; \
BignumDblInt ADC_temp = (BignumInt)(a); \
ADC_temp += (BignumInt)(b); \
ADC_temp += (c); \
(ret) = (BignumInt)ADC_temp; \
(retc) = (BignumCarry)(ADC_temp >> BIGNUM_INT_BITS); \
} while (0)
#define BignumMUL(rh, rl, a, b) do \
{ \
DEFINE_BIGNUMDBLINT; \
BignumDblInt MUL_temp = (BignumInt)(a); \
MUL_temp *= (BignumInt)(b); \
(rh) = (BignumInt)(MUL_temp >> BIGNUM_INT_BITS); \
(rl) = (BignumInt)(MUL_temp); \
} while (0)
#define BignumMULADD(rh, rl, a, b, addend) do \
{ \
DEFINE_BIGNUMDBLINT; \
BignumDblInt MUL_temp = (BignumInt)(a); \
MUL_temp *= (BignumInt)(b); \
MUL_temp += (BignumInt)(addend); \
(rh) = (BignumInt)(MUL_temp >> BIGNUM_INT_BITS); \
(rl) = (BignumInt)(MUL_temp); \
} while (0)
#define BignumMULADD2(rh, rl, a, b, addend1, addend2) do \
{ \
DEFINE_BIGNUMDBLINT; \
BignumDblInt MUL_temp = (BignumInt)(a); \
MUL_temp *= (BignumInt)(b); \
MUL_temp += (BignumInt)(addend1); \
MUL_temp += (BignumInt)(addend2); \
(rh) = (BignumInt)(MUL_temp >> BIGNUM_INT_BITS); \
(rl) = (BignumInt)(MUL_temp); \
} while (0)
#endif /* DEFINE_BIGNUMDBLINT */
/* ----------------------------------------------------------------------
* Data structures used inside bignum.c.
*/
struct mp_int {
size_t nw;
BignumInt *w;
};
struct MontyContext {
/*
* The actual modulus.
*/
mp_int *m;
/*
* Montgomery multiplication works by selecting a value r > m,
* coprime to m, which is really easy to divide by. In binary
* arithmetic, that means making it a power of 2; in fact we make
* it a whole number of BignumInt.
*
* We don't store r directly as an mp_int (there's no need). But
* its value is 2^rbits; we also store rw = rbits/BIGNUM_INT_BITS
* (the corresponding word offset within an mp_int).
*
* pw is the number of words needed to store an mp_int you're
* doing reduction on: it has to be big enough to hold the sum of
* an input value up to m^2 plus an extra addend up to m*r.
*/
size_t rbits, rw, pw;
/*
* The key step in Montgomery reduction requires the inverse of -m
* mod r.
*/
mp_int *minus_minv_mod_r;
/*
* r^1, r^2 and r^3 mod m, which are used for various purposes.
*
* (Annoyingly, this is one of the rare cases where it would have
* been nicer to have a Pascal-style 1-indexed array. I couldn't
* _quite_ bring myself to put a gratuitous zero element in here.
* So you just have to live with getting r^k by taking the [k-1]th
* element of this array.)
*/
mp_int *powers_of_r_mod_m[3];
/*
* Persistent scratch space from which monty_* functions can
* allocate storage for intermediate values.
*/
mp_int *scratch;
};
/* Functions shared between mpint.c and mpunsafe.c */
mp_int *mp_make_sized(size_t nw);
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