X-Git-Url: https://git.distorted.org.uk/u/mdw/putty/blobdiff_plain/736cc6d131e571cd9a0d3f2b5b5dc9ab493d207a..819a22b356a0113860c30b12cf42ba8616a15d1a:/sshbn.c diff --git a/sshbn.c b/sshbn.c index 2d8359e3..728b6fa0 100644 --- a/sshbn.c +++ b/sshbn.c @@ -3,11 +3,26 @@ */ #include +#include #include #include #include "misc.h" +/* + * Usage notes: + * * Do not call the DIVMOD_WORD macro with expressions such as array + * subscripts, as some implementations object to this (see below). + * * Note that none of the division methods below will cope if the + * quotient won't fit into BIGNUM_INT_BITS. Callers should be careful + * to avoid this case. + * If this condition occurs, in the case of the x86 DIV instruction, + * an overflow exception will occur, which (according to a correspondent) + * will manifest on Windows as something like + * 0xC0000095: Integer overflow + * The C variant won't give the right answer, either. + */ + #if defined __GNUC__ && defined __i386__ typedef unsigned long BignumInt; typedef unsigned long long BignumDblInt; @@ -19,6 +34,23 @@ typedef unsigned long long BignumDblInt; __asm__("div %2" : \ "=d" (r), "=a" (q) : \ "r" (w), "d" (hi), "a" (lo)) +#elif defined _MSC_VER && defined _M_IX86 +typedef unsigned __int32 BignumInt; +typedef unsigned __int64 BignumDblInt; +#define BIGNUM_INT_MASK 0xFFFFFFFFUL +#define BIGNUM_TOP_BIT 0x80000000UL +#define BIGNUM_INT_BITS 32 +#define MUL_WORD(w1, w2) ((BignumDblInt)w1 * w2) +/* Note: MASM interprets array subscripts in the macro arguments as + * assembler syntax, which gives the wrong answer. Don't supply them. + * */ +#define DIVMOD_WORD(q, r, hi, lo, w) do { \ + __asm mov edx, hi \ + __asm mov eax, lo \ + __asm div w \ + __asm mov r, edx \ + __asm mov q, eax \ +} while(0) #else typedef unsigned short BignumInt; typedef unsigned long BignumDblInt; @@ -133,7 +165,7 @@ static void internal_add_shifted(BignumInt *number, int bshift = shift % BIGNUM_INT_BITS; BignumDblInt addend; - addend = n << bshift; + addend = (BignumDblInt)n << bshift; while (addend) { addend += number[word]; @@ -184,17 +216,39 @@ static void internal_mod(BignumInt *a, int alen, ai1 = a[i + 1]; /* Find q = h:a[i] / m0 */ - DIVMOD_WORD(q, r, h, a[i], m0); - - /* Refine our estimate of q by looking at - h:a[i]:a[i+1] / m0:m1 */ - t = MUL_WORD(m1, q); - if (t > ((BignumDblInt) r << BIGNUM_INT_BITS) + ai1) { - q--; - t -= m1; - r = (r + m0) & BIGNUM_INT_MASK; /* overflow? */ - if (r >= (BignumDblInt) m0 && - t > ((BignumDblInt) r << BIGNUM_INT_BITS) + ai1) q--; + if (h >= m0) { + /* + * Special case. + * + * To illustrate it, suppose a BignumInt is 8 bits, and + * we are dividing (say) A1:23:45:67 by A1:B2:C3. Then + * our initial division will be 0xA123 / 0xA1, which + * will give a quotient of 0x100 and a divide overflow. + * However, the invariants in this division algorithm + * are not violated, since the full number A1:23:... is + * _less_ than the quotient prefix A1:B2:... and so the + * following correction loop would have sorted it out. + * + * In this situation we set q to be the largest + * quotient we _can_ stomach (0xFF, of course). + */ + q = BIGNUM_INT_MASK; + } else { + /* Macro doesn't want an array subscript expression passed + * into it (see definition), so use a temporary. */ + BignumInt tmplo = a[i]; + DIVMOD_WORD(q, r, h, tmplo, m0); + + /* Refine our estimate of q by looking at + h:a[i]:a[i+1] / m0:m1 */ + t = MUL_WORD(m1, q); + if (t > ((BignumDblInt) r << BIGNUM_INT_BITS) + ai1) { + q--; + t -= m1; + r = (r + m0) & BIGNUM_INT_MASK; /* overflow? */ + if (r >= (BignumDblInt) m0 && + t > ((BignumDblInt) r << BIGNUM_INT_BITS) + ai1) q--; + } } /* Subtract q * m from a[i...] */ @@ -226,16 +280,25 @@ static void internal_mod(BignumInt *a, int alen, /* * Compute (base ^ exp) % mod. - * The base MUST be smaller than the modulus. - * The most significant word of mod MUST be non-zero. - * We assume that the result array is the same size as the mod array. */ -Bignum modpow(Bignum base, Bignum exp, Bignum mod) +Bignum modpow(Bignum base_in, Bignum exp, Bignum mod) { BignumInt *a, *b, *n, *m; int mshift; int mlen, i, j; - Bignum result; + Bignum base, result; + + /* + * The most significant word of mod needs to be non-zero. It + * should already be, but let's make sure. + */ + assert(mod[mod[0]] != 0); + + /* + * Make sure the base is smaller than the modulus, by reducing + * it modulo the modulus if not. + */ + base = bigmod(base_in, mod); /* Allocate m of size mlen, copy mod to m */ /* We use big endian internally */ @@ -331,6 +394,8 @@ Bignum modpow(Bignum base, Bignum exp, Bignum mod) n[i] = 0; sfree(n); + freebn(base); + return result; } @@ -527,20 +592,26 @@ Bignum bignum_from_bytes(const unsigned char *data, int nbytes) } /* - * Read an ssh1-format bignum from a data buffer. Return the number - * of bytes consumed. + * Read an SSH-1-format bignum from a data buffer. Return the number + * of bytes consumed, or -1 if there wasn't enough data. */ -int ssh1_read_bignum(const unsigned char *data, Bignum * result) +int ssh1_read_bignum(const unsigned char *data, int len, Bignum * result) { const unsigned char *p = data; int i; int w, b; + if (len < 2) + return -1; + w = 0; for (i = 0; i < 2; i++) w = (w << 8) + *p++; b = (w + 7) / 8; /* bits -> bytes */ + if (len < b+2) + return -1; + if (!result) /* just return length */ return b + 2; @@ -550,7 +621,7 @@ int ssh1_read_bignum(const unsigned char *data, Bignum * result) } /* - * Return the bit count of a bignum, for ssh1 encoding. + * Return the bit count of a bignum, for SSH-1 encoding. */ int bignum_bitcount(Bignum bn) { @@ -561,7 +632,7 @@ int bignum_bitcount(Bignum bn) } /* - * Return the byte length of a bignum when ssh1 encoded. + * Return the byte length of a bignum when SSH-1 encoded. */ int ssh1_bignum_length(Bignum bn) { @@ -569,7 +640,7 @@ int ssh1_bignum_length(Bignum bn) } /* - * Return the byte length of a bignum when ssh2 encoded. + * Return the byte length of a bignum when SSH-2 encoded. */ int ssh2_bignum_length(Bignum bn) { @@ -617,7 +688,7 @@ void bignum_set_bit(Bignum bn, int bitnum, int value) } /* - * Write a ssh1-format bignum into a buffer. It is assumed the + * Write a SSH-1-format bignum into a buffer. It is assumed the * buffer is big enough. Returns the number of bytes used. */ int ssh1_write_bignum(void *data, Bignum bn) @@ -729,6 +800,7 @@ Bignum bigmuladd(Bignum a, Bignum b, Bignum addend) } ret[0] = maxspot; + sfree(workspace); return ret; } @@ -908,6 +980,7 @@ Bignum modinv(Bignum number, Bignum modulus) x = bigmuladd(q, xp, t); sign = -sign; freebn(t); + freebn(q); } freebn(b); @@ -1009,5 +1082,6 @@ char *bignum_decimal(Bignum x) /* * Done. */ + sfree(workspace); return ret; }