[PATCH v4 4/6] lib: rsa: generate additional parameters for public key
Heinrich Schuchardt
xypron.glpk at gmx.de
Wed Jan 8 19:16:10 CET 2020
On 1/8/20 7:07 PM, Heinrich Schuchardt wrote:
>
>
> On 11/21/19 1:11 AM, AKASHI Takahiro wrote:
>> In the current implementation of FIT_SIGNATURE, five parameters for
>> a RSA public key are required while only two of them are essential.
>> (See rsa-mod-exp.h and uImage.FIT/signature.txt)
>> This is a result of considering relatively limited computer power
>> and resources on embedded systems, while such a assumption may not
>> be quite practical for other use cases.
>>
>> In this patch, added is a function, rsa_gen_key_prop(), which will
>> generate additional parameters for other uses, in particular
>> UEFI secure boot, on the fly.
>>
>> Note: the current code uses some "big number" rouKtines from BearSSL
>> for the calculation.
>>
>> Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
>> ---
>> include/u-boot/rsa-mod-exp.h | 23 ++
>> lib/rsa/Kconfig | 1 +
>> lib/rsa/Makefile | 1 +
>> lib/rsa/rsa-keyprop.c | 725 +++++++++++++++++++++++++++++++++++
>> 4 files changed, 750 insertions(+)
>> create mode 100644 lib/rsa/rsa-keyprop.c
>>
>> diff --git a/include/u-boot/rsa-mod-exp.h b/include/u-boot/rsa-mod-exp.h
>> index 8a428c4b6a1a..1da8af1bb83d 100644
>> --- a/include/u-boot/rsa-mod-exp.h
>> +++ b/include/u-boot/rsa-mod-exp.h
>> @@ -26,6 +26,29 @@ struct key_prop {
>> uint32_t exp_len; /* Exponent length in number of uint8_t */
>> };
>>
>> +/**
>> + * rsa_gen_key_prop() - Generate key properties of RSA public key
>> + * @key: Specifies key data in DER format
>> + * @keylen: Length of @key
>> + * @prop: Generated key property
>> + *
>> + * This function takes a blob of encoded RSA public key data in DER
>> + * format, parse it and generate all the relevant properties
>> + * in key_prop structure.
>> + * Return a pointer to struct key_prop in @prop on success.
>> + *
>> + * Return: 0 on success, negative on error
>> + */
>> +int rsa_gen_key_prop(const void *key, uint32_t keylen, struct
>> key_prop **proc);
>> +
>> +/**
>> + * rsa_free_key_prop() - Free key properties
>> + * @prop: Pointer to struct key_prop
>> + *
>> + * This function frees all the memories allocated by rsa_gen_key_prop().
>> + */
>> +void rsa_free_key_prop(struct key_prop *prop);
>> +
>> /**
>> * rsa_mod_exp_sw() - Perform RSA Modular Exponentiation in sw
>> *
>> diff --git a/lib/rsa/Kconfig b/lib/rsa/Kconfig
>> index 71e4c06bf883..d1d6f6cf64a3 100644
>> --- a/lib/rsa/Kconfig
>> +++ b/lib/rsa/Kconfig
>> @@ -33,6 +33,7 @@ config RSA_VERIFY
>> config RSA_VERIFY_WITH_PKEY
>> bool "Execute RSA verification without key parameters from FDT"
>> depends on RSA
>> + imply RSA_PUBLIC_KEY_PARSER
>
> Do we really need RSA_PUBLIC_KEY_PARSER whenever we use CONFIG_RSA=y?
> E.g. on a system without the UEFI sub-system?
>
> Otherwise simply let RSA_PUBLIC_KEY_PARSER depend on RSA.
>
>> help
>> The standard RSA-signature verification code (FIT_SIGNATURE) uses
>> pre-calculated key properties, that are stored in fdt blob, in
>> diff --git a/lib/rsa/Makefile b/lib/rsa/Makefile
>> index c07305188e0c..14ed3cb4012b 100644
>> --- a/lib/rsa/Makefile
>> +++ b/lib/rsa/Makefile
>> @@ -6,4 +6,5 @@
>> # Wolfgang Denk, DENX Software Engineering, wd at denx.de.
>>
>> obj-$(CONFIG_$(SPL_)RSA_VERIFY) += rsa-verify.o rsa-checksum.o
>> +obj-$(CONFIG_RSA_VERIFY_WITH_PKEY) += rsa-keyprop.o
>> obj-$(CONFIG_RSA_SOFTWARE_EXP) += rsa-mod-exp.o
>> diff --git a/lib/rsa/rsa-keyprop.c b/lib/rsa/rsa-keyprop.c
>> new file mode 100644
>> index 000000000000..9464df009343
>> --- /dev/null
>> +++ b/lib/rsa/rsa-keyprop.c
>> @@ -0,0 +1,725 @@
>> +// SPDX-License-Identifier: GPL-2.0+ and MIT
>> +/*
>> + * RSA library - generate parameters for a public key
>> + *
>> + * Copyright (c) 2019 Linaro Limited
>> + * Author: AKASHI Takahiro
>> + *
>> + * Big number routines in this file come from BearSSL:
>> + * Copyright (c) 2016 Thomas Pornin <pornin at bolet.org>
>> + */
>> +
>> +#include <common.h>
>> +#include <image.h>
>> +#include <malloc.h>
>> +#include <asm/byteorder.h>
>> +#include <crypto/internal/rsa.h>
>> +#include <u-boot/rsa-mod-exp.h>
>> +
>> +/**
>> + * br_dec16be() - Convert 16-bit big-endian integer to native
>> + * @src: Pointer to data
>> + * Return: Native-endian integer
>> + */
>> +static unsigned br_dec16be(const void *src)
>> +{
>> + return be16_to_cpup(src);
>> +}
>> +
>> +/**
>> + * br_dec32be() - Convert 32-bit big-endian integer to native
>> + * @src: Pointer to data
>> + * Return: Native-endian integer
>> + */
>> +static uint32_t br_dec32be(const void *src)
>> +{
>> + return be32_to_cpup(src);
>> +}
>> +
>> +/**
>> + * br_enc32be() - Convert native 32-bit integer to big-endian
>> + * @dst: Pointer to buffer to store big-endian integer in
>> + * @x: Native 32-bit integer
>> + */
>> +static void br_enc32be(void *dst, uint32_t x)
>> +{
>> + __be32 tmp;
>> +
>> + tmp = cpu_to_be32(x);
>> + memcpy(dst, &tmp, sizeof(tmp));
>> +}
>> +
>> +/* from BearSSL's src/inner.h */
>> +
>> +/*
>> + * Negate a boolean.
>> + */
>> +static uint32_t NOT(uint32_t ctl)
>> +{
>> + return ctl ^ 1;
>> +}
>> +
>> +/*
>> + * Multiplexer: returns x if ctl == 1, y if ctl == 0.
>> + */
>> +static uint32_t MUX(uint32_t ctl, uint32_t x, uint32_t y)
>> +{
>> + return y ^ (-ctl & (x ^ y));
>> +}
>> +
>> +/*
>> + * Equality check: returns 1 if x == y, 0 otherwise.
>> + */
>> +static uint32_t EQ(uint32_t x, uint32_t y)
>> +{
>> + uint32_t q;
>> +
>> + q = x ^ y;
>> + return NOT((q | -q) >> 31);
>> +}
>> +
>> +/*
>> + * Inequality check: returns 1 if x != y, 0 otherwise.
>> + */
>> +static uint32_t NEQ(uint32_t x, uint32_t y)
>> +{
>> + uint32_t q;
>> +
>> + q = x ^ y;
>> + return (q | -q) >> 31;
>
> We want to minimize the code size of U-Boot.
>
> So, please, review this code and remove all of this bogus.
Are timing attacks relevant in any of our UEFI use cases?
I thought we only are verifying signatures against public keys that are
anyway in reach of an adversery.
Best regards
Heinrich
>
>> +}
>> +
>> +/*
>> + * Comparison: returns 1 if x > y, 0 otherwise.
>> + */
>> +static uint32_t GT(uint32_t x, uint32_t y)
>> +{
>> + /*
>> + * If both x < 2^31 and y < 2^31, then y-x will have its high
>> + * bit set if x > y, cleared otherwise.
>> + *
>> + * If either x >= 2^31 or y >= 2^31 (but not both), then the
>> + * result is the high bit of x.
>> + *
>> + * If both x >= 2^31 and y >= 2^31, then we can virtually
>> + * subtract 2^31 from both, and we are back to the first case.
>> + * Since (y-2^31)-(x-2^31) = y-x, the subtraction is already
>> + * fine.
>> + */
>> + uint32_t z;
>> +
>> + z = y - x;
>> + return (z ^ ((x ^ y) & (x ^ z))) >> 31;
>> +}
>> +
>> +/*
>> + * Compute the bit length of a 32-bit integer. Returned value is
>> between 0
>> + * and 32 (inclusive).
>> + */
>> +static uint32_t BIT_LENGTH(uint32_t x)
>> +{
>> + uint32_t k, c;
>> +
>> + k = NEQ(x, 0);
>> + c = GT(x, 0xFFFF); x = MUX(c, x >> 16, x); k += c << 4;
>> + c = GT(x, 0x00FF); x = MUX(c, x >> 8, x); k += c << 3;
>> + c = GT(x, 0x000F); x = MUX(c, x >> 4, x); k += c << 2;
>> + c = GT(x, 0x0003); x = MUX(c, x >> 2, x); k += c << 1;
>> + k += GT(x, 0x0001);
>> + return k;
>> +}
>> +
>> +#define GE(x, y) NOT(GT(y, x))
>> +#define LT(x, y) GT(y, x)
>> +#define MUL(x, y) ((uint64_t)(x) * (uint64_t)(y))
>> +
>> +/*
>> + * Integers 'i32'
>> + * --------------
>> + *
>> + * The 'i32' functions implement computations on big integers using
>> + * an internal representation as an array of 32-bit integers. For
>> + * an array x[]:
>> + * -- x[0] contains the "announced bit length" of the integer
>> + * -- x[1], x[2]... contain the value in little-endian order (x[1]
>> + * contains the least significant 32 bits)
>> + *
>> + * Multiplications rely on the elementary 32x32->64 multiplication.
>> + *
>> + * The announced bit length specifies the number of bits that are
>> + * significant in the subsequent 32-bit words. Unused bits in the
>> + * last (most significant) word are set to 0; subsequent words are
>> + * uninitialized and need not exist at all.
>> + *
>> + * The execution time and memory access patterns of all computations
>> + * depend on the announced bit length, but not on the actual word
>> + * values. For modular integers, the announced bit length of any integer
>> + * modulo n is equal to the actual bit length of n; thus, computations
>> + * on modular integers are "constant-time" (only the modulus length may
>> + * leak).
>> + */
>> +
>> +/*
>> + * Extract one word from an integer. The offset is counted in bits.
>> + * The word MUST entirely fit within the word elements corresponding
>> + * to the announced bit length of a[].
>> + */
>> +static uint32_t br_i32_word(const uint32_t *a, uint32_t off)
>> +{
>> + size_t u;
>> + unsigned j;
>> +
>> + u = (size_t)(off >> 5) + 1;
>> + j = (unsigned)off & 31;
>> + if (j == 0) {
>> + return a[u];
>> + } else {
>> + return (a[u] >> j) | (a[u + 1] << (32 - j));
>> + }
>> +}
>> +
>> +/* from BearSSL's src/int/i32_bitlen.c */
>> +
>> +/*
>> + * Compute the actual bit length of an integer. The argument x should
>> + * point to the first (least significant) value word of the integer.
>> + * The len 'xlen' contains the number of 32-bit words to access.
>> + *
>> + * CT: value or length of x does not leak.
>> + */
>> +static uint32_t br_i32_bit_length(uint32_t *x, size_t xlen)
>> +{
>> + uint32_t tw, twk;
>> +
>> + tw = 0;
>> + twk = 0;
>> + while (xlen -- > 0) {
>> + uint32_t w, c;
>> +
>> + c = EQ(tw, 0);
>> + w = x[xlen];
>> + tw = MUX(c, w, tw);
>> + twk = MUX(c, (uint32_t)xlen, twk);
>> + }
>> + return (twk << 5) + BIT_LENGTH(tw);
>> +}
>> +
>> +/* from BearSSL's src/int/i32_decode.c */
>> +
>> +/*
>> + * Decode an integer from its big-endian unsigned representation. The
>> + * "true" bit length of the integer is computed, but all words of x[]
>> + * corresponding to the full 'len' bytes of the source are set.
>> + *
>> + * CT: value or length of x does not leak.
>> + */
>> +static void br_i32_decode(uint32_t *x, const void *src, size_t len)
>> +{
>> + const unsigned char *buf;
>> + size_t u, v;
>> +
>> + buf = src;
>> + u = len;
>> + v = 1;
>> + for (;;) {
>> + if (u < 4) {
>> + uint32_t w;
>> +
>> + if (u < 2) {
>> + if (u == 0) {
>> + break;
>> + } else {
>> + w = buf[0];
>> + }
>> + } else {
>> + if (u == 2) {
>> + w = br_dec16be(buf);
>> + } else {
>> + w = ((uint32_t)buf[0] << 16)
>> + | br_dec16be(buf + 1);
>> + }
>> + }
>> + x[v ++] = w;
>> + break;
>> + } else {
>> + u -= 4;
>> + x[v ++] = br_dec32be(buf + u);
>> + }
>> + }
>> + x[0] = br_i32_bit_length(x + 1, v - 1);
>> +}
>> +
>> +/* from BearSSL's src/int/i32_encode.c */
>> +
>> +/*
>> + * Encode an integer into its big-endian unsigned representation. The
>> + * output length in bytes is provided (parameter 'len'); if the length
>> + * is too short then the integer is appropriately truncated; if it is
>> + * too long then the extra bytes are set to 0.
>> + */
>> +static void br_i32_encode(void *dst, size_t len, const uint32_t *x)
>> +{
>> + unsigned char *buf;
>> + size_t k;
>> +
>> + buf = dst;
>> +
>> + /*
>> + * Compute the announced size of x in bytes; extra bytes are
>> + * filled with zeros.
>> + */
>> + k = (x[0] + 7) >> 3;
>> + while (len > k) {
>> + *buf ++ = 0;
>> + len --;
>> + }
>> +
>> + /*
>> + * Now we use k as index within x[]. That index starts at 1;
>> + * we initialize it to the topmost complete word, and process
>> + * any remaining incomplete word.
>> + */
>> + k = (len + 3) >> 2;
>> + switch (len & 3) {
>> + case 3:
>> + *buf ++ = x[k] >> 16;
>> + /* fall through */
>> + case 2:
>> + *buf ++ = x[k] >> 8;
>> + /* fall through */
>> + case 1:
>> + *buf ++ = x[k];
>> + k --;
>> + }
>> +
>> + /*
>> + * Encode all complete words.
>> + */
>> + while (k > 0) {
>> + br_enc32be(buf, x[k]);
>> + k --;
>> + buf += 4;
>> + }
>> +}
>> +
>> +/* from BearSSL's src/int/i32_ninv32.c */
>> +
>> +/*
>> + * Compute -(1/x) mod 2^32. If x is even, then this function returns 0.
>> + */
>> +static uint32_t br_i32_ninv32(uint32_t x)
>> +{
>> + uint32_t y;
>> +
>> + y = 2 - x;
>> + y *= 2 - y * x;
>> + y *= 2 - y * x;
>> + y *= 2 - y * x;
>> + y *= 2 - y * x;
>> + return MUX(x & 1, -y, 0);
>> +}
>> +
>> +/* from BearSSL's src/int/i32_add.c */
>> +
>> +/*
>> + * Add b[] to a[] and return the carry (0 or 1). If ctl is 0, then a[]
>> + * is unmodified, but the carry is still computed and returned. The
>> + * arrays a[] and b[] MUST have the same announced bit length.
>> + *
>> + * a[] and b[] MAY be the same array, but partial overlap is not
>> allowed.
>> + */
>> +static uint32_t br_i32_add(uint32_t *a, const uint32_t *b, uint32_t ctl)
>> +{
>> + uint32_t cc;
>> + size_t u, m;
>> +
>> + cc = 0;
>> + m = (a[0] + 63) >> 5;
>> + for (u = 1; u < m; u ++) {
>> + uint32_t aw, bw, naw;
>> +
>> + aw = a[u];
>> + bw = b[u];
>> + naw = aw + bw + cc;
>> +
>> + /*
>> + * Carry is 1 if naw < aw. Carry is also 1 if naw == aw
>> + * AND the carry was already 1.
>> + */
>> + cc = (cc & EQ(naw, aw)) | LT(naw, aw);
>> + a[u] = MUX(ctl, naw, aw);
>> + }
>> + return cc;
>> +}
>> +
>> +/* from BearSSL's src/int/i32_sub.c */
>> +
>> +/*
>> + * Subtract b[] from a[] and return the carry (0 or 1). If ctl is 0,
>> + * then a[] is unmodified, but the carry is still computed and returned.
>> + * The arrays a[] and b[] MUST have the same announced bit length.
>> + *
>> + * a[] and b[] MAY be the same array, but partial overlap is not
>> allowed.
>> + */
>> +static uint32_t br_i32_sub(uint32_t *a, const uint32_t *b, uint32_t ctl)
>> +{
>> + uint32_t cc;
>> + size_t u, m;
>> +
>> + cc = 0;
>> + m = (a[0] + 63) >> 5;
>> + for (u = 1; u < m; u ++) {
>> + uint32_t aw, bw, naw;
>> +
>> + aw = a[u];
>> + bw = b[u];
>> + naw = aw - bw - cc;
>> +
>> + /*
>> + * Carry is 1 if naw > aw. Carry is 1 also if naw == aw
>> + * AND the carry was already 1.
>> + */
>> + cc = (cc & EQ(naw, aw)) | GT(naw, aw);
>> + a[u] = MUX(ctl, naw, aw);
>> + }
>> + return cc;
>> +}
>> +
>> +/* from BearSSL's src/int/i32_div32.c */
>> +
>> +/*
>> + * Constant-time division. The dividend hi:lo is divided by the
>> + * divisor d; the quotient is returned and the remainder is written
>> + * in *r. If hi == d, then the quotient does not fit on 32 bits;
>> + * returned value is thus truncated. If hi > d, returned values are
>> + * indeterminate.
>> + */
>> +static uint32_t br_divrem(uint32_t hi, uint32_t lo, uint32_t d,
>> uint32_t *r)
>> +{
>> + /* TODO: optimize this */
>> + uint32_t q;
>> + uint32_t ch, cf;
>> + int k;
>> +
>> + q = 0;
>> + ch = EQ(hi, d);
>> + hi = MUX(ch, 0, hi);
>> + for (k = 31; k > 0; k --) {
>> + int j;
>> + uint32_t w, ctl, hi2, lo2;
>> +
>> + j = 32 - k;
>> + w = (hi << j) | (lo >> k);
>> + ctl = GE(w, d) | (hi >> k);
>> + hi2 = (w - d) >> j;
>> + lo2 = lo - (d << k);
>> + hi = MUX(ctl, hi2, hi);
>> + lo = MUX(ctl, lo2, lo);
>> + q |= ctl << k;
>> + }
>> + cf = GE(lo, d) | hi;
>> + q |= cf;
>> + *r = MUX(cf, lo - d, lo);
>> + return q;
>> +}
>> +
>> +/*
>> + * Wrapper for br_divrem(); the remainder is returned, and the quotient
>> + * is discarded.
>> + */
>> +static uint32_t br_rem(uint32_t hi, uint32_t lo, uint32_t d)
>> +{
>> + uint32_t r;
>> +
>> + br_divrem(hi, lo, d, &r);
>> + return r;
>> +}
>> +
>> +/*
>> + * Wrapper for br_divrem(); the quotient is returned, and the remainder
>> + * is discarded.
>> + */
>> +static uint32_t br_div(uint32_t hi, uint32_t lo, uint32_t d)
>> +{
>> + uint32_t r;
>> +
>> + return br_divrem(hi, lo, d, &r);
>> +}
>> +
>> +/* from BearSSL's src/int/i32_muladd.c */
>> +
>> +/*
>> + * Multiply x[] by 2^32 and then add integer z, modulo m[]. This
>> + * function assumes that x[] and m[] have the same announced bit
>> + * length, and the announced bit length of m[] matches its true
>> + * bit length.
>> + *
>> + * x[] and m[] MUST be distinct arrays.
>> + *
>> + * CT: only the common announced bit length of x and m leaks, not
>> + * the values of x, z or m.
>> + */
>> +static void br_i32_muladd_small(uint32_t *x, uint32_t z, const
>> uint32_t *m)
>> +{
>> + uint32_t m_bitlen;
>> + size_t u, mlen;
>> + uint32_t a0, a1, b0, hi, g, q, tb;
>> + uint32_t chf, clow, under, over;
>> + uint64_t cc;
>> +
>> + /*
>> + * We can test on the modulus bit length since we accept to
>> + * leak that length.
>> + */
>> + m_bitlen = m[0];
>> + if (m_bitlen == 0) {
>> + return;
>> + }
>> + if (m_bitlen <= 32) {
>> + x[1] = br_rem(x[1], z, m[1]);
>> + return;
>> + }
>> + mlen = (m_bitlen + 31) >> 5;
>> +
>> + /*
>> + * Principle: we estimate the quotient (x*2^32+z)/m by
>> + * doing a 64/32 division with the high words.
>> + *
>> + * Let:
>> + * w = 2^32
>> + * a = (w*a0 + a1) * w^N + a2
>> + * b = b0 * w^N + b2
>> + * such that:
>> + * 0 <= a0 < w
>> + * 0 <= a1 < w
>> + * 0 <= a2 < w^N
>> + * w/2 <= b0 < w
>> + * 0 <= b2 < w^N
>> + * a < w*b
>> + * I.e. the two top words of a are a0:a1, the top word of b is
>> + * b0, we ensured that b0 is "full" (high bit set), and a is
>> + * such that the quotient q = a/b fits on one word (0 <= q < w).
>> + *
>> + * If a = b*q + r (with 0 <= r < q), we can estimate q by
>> + * doing an Euclidean division on the top words:
>> + * a0*w+a1 = b0*u + v (with 0 <= v < w)
>> + * Then the following holds:
>> + * 0 <= u <= w
>> + * u-2 <= q <= u
>> + */
>> + a0 = br_i32_word(x, m_bitlen - 32);
>> + hi = x[mlen];
>> + memmove(x + 2, x + 1, (mlen - 1) * sizeof *x);
>> + x[1] = z;
>> + a1 = br_i32_word(x, m_bitlen - 32);
>> + b0 = br_i32_word(m, m_bitlen - 32);
>> +
>> + /*
>> + * We estimate a divisor q. If the quotient returned by br_div()
>> + * is g:
>> + * -- If a0 == b0 then g == 0; we want q = 0xFFFFFFFF.
>> + * -- Otherwise:
>> + * -- if g == 0 then we set q = 0;
>> + * -- otherwise, we set q = g - 1.
>> + * The properties described above then ensure that the true
>> + * quotient is q-1, q or q+1.
>> + */
>> + g = br_div(a0, a1, b0);
>> + q = MUX(EQ(a0, b0), 0xFFFFFFFF, MUX(EQ(g, 0), 0, g - 1));
>> +
>> + /*
>> + * We subtract q*m from x (with the extra high word of value 'hi').
>> + * Since q may be off by 1 (in either direction), we may have to
>> + * add or subtract m afterwards.
>> + *
>> + * The 'tb' flag will be true (1) at the end of the loop if the
>> + * result is greater than or equal to the modulus (not counting
>> + * 'hi' or the carry).
>> + */
>> + cc = 0;
>> + tb = 1;
>> + for (u = 1; u <= mlen; u ++) {
>> + uint32_t mw, zw, xw, nxw;
>> + uint64_t zl;
>> +
>> + mw = m[u];
>> + zl = MUL(mw, q) + cc;
>> + cc = (uint32_t)(zl >> 32);
>> + zw = (uint32_t)zl;
>> + xw = x[u];
>> + nxw = xw - zw;
>> + cc += (uint64_t)GT(nxw, xw);
>> + x[u] = nxw;
>> + tb = MUX(EQ(nxw, mw), tb, GT(nxw, mw));
>> + }
>> +
>> + /*
>> + * If we underestimated q, then either cc < hi (one extra bit
>> + * beyond the top array word), or cc == hi and tb is true (no
>> + * extra bit, but the result is not lower than the modulus). In
>> + * these cases we must subtract m once.
>> + *
>> + * Otherwise, we may have overestimated, which will show as
>> + * cc > hi (thus a negative result). Correction is adding m once.
>> + */
>> + chf = (uint32_t)(cc >> 32);
>> + clow = (uint32_t)cc;
>> + over = chf | GT(clow, hi);
>> + under = ~over & (tb | (~chf & LT(clow, hi)));
>> + br_i32_add(x, m, over);
>> + br_i32_sub(x, m, under);
>> +}
>> +
>> +/* from BearSSL's src/int/i32_reduce.c */
>> +
>> +/*
>> + * Reduce an integer (a[]) modulo another (m[]). The result is written
>> + * in x[] and its announced bit length is set to be equal to that of
>> m[].
>> + *
>> + * x[] MUST be distinct from a[] and m[].
>> + *
>> + * CT: only announced bit lengths leak, not values of x, a or m.
>> + */
>> +static void br_i32_reduce(uint32_t *x, const uint32_t *a, const
>> uint32_t *m)
>> +{
>> + uint32_t m_bitlen, a_bitlen;
>> + size_t mlen, alen, u;
>> +
>> + m_bitlen = m[0];
>> + mlen = (m_bitlen + 31) >> 5;
>> +
>> + x[0] = m_bitlen;
>> + if (m_bitlen == 0) {
>> + return;
>> + }
>> +
>> + /*
>> + * If the source is shorter, then simply copy all words from a[]
>> + * and zero out the upper words.
>> + */
>> + a_bitlen = a[0];
>> + alen = (a_bitlen + 31) >> 5;
>> + if (a_bitlen < m_bitlen) {
>> + memcpy(x + 1, a + 1, alen * sizeof *a);
>> + for (u = alen; u < mlen; u ++) {
>> + x[u + 1] = 0;
>> + }
>> + return;
>> + }
>> +
>> + /*
>> + * The source length is at least equal to that of the modulus.
>> + * We must thus copy N-1 words, and input the remaining words
>> + * one by one.
>> + */
>> + memcpy(x + 1, a + 2 + (alen - mlen), (mlen - 1) * sizeof *a);
>> + x[mlen] = 0;
>> + for (u = 1 + alen - mlen; u > 0; u --) {
>> + br_i32_muladd_small(x, a[u], m);
>> + }
>> +}
>> +
>> +/**
>> + * rsa_free_key_prop() - Free key properties
>> + * @prop: Pointer to struct key_prop
>> + *
>> + * This function frees all the memories allocated by rsa_gen_key_prop().
>> + */
>> +void rsa_free_key_prop(struct key_prop *prop)
>> +{
>> + if (!prop)
>> + return;
>> +
>> + free((void *)prop->modulus);
>> + free((void *)prop->public_exponent);
>> + free((void *)prop->rr);
>> +
>> + free(prop);
>> +}
>> +
>> +/**
>> + * rsa_gen_key_prop() - Generate key properties of RSA public key
>> + * @key: Specifies key data in DER format
>> + * @keylen: Length of @key
>> + * @prop: Generated key property
>> + *
>> + * This function takes a blob of encoded RSA public key data in DER
>> + * format, parse it and generate all the relevant properties
>> + * in key_prop structure.
>> + * Return a pointer to struct key_prop in @prop on success.
>> + *
>> + * Return: 0 on success, negative on error
>> + */
>> +int rsa_gen_key_prop(const void *key, uint32_t keylen, struct
>> key_prop **prop)
>> +{
>> + struct rsa_key rsa_key;
>> + uint32_t *n = NULL, *rr = NULL, *rrtmp = NULL;
>> + const int max_rsa_size = 4096;
>> + int rlen, i, ret;
>> +
>> + *prop = calloc(sizeof(**prop), 1);
>> + n = calloc(sizeof(uint32_t), 1 + (max_rsa_size >> 5));
>> + rr = calloc(sizeof(uint32_t), 1 + (max_rsa_size >> 5));
>> + rrtmp = calloc(sizeof(uint32_t), 1 + (max_rsa_size >> 5));
>> + if (!(*prop) || !n || !rr || !rrtmp) {
>> + ret = -ENOMEM;
>> + goto err;
>> + }
>> +
>> + ret = rsa_parse_pub_key(&rsa_key, key, keylen);
>> + if (ret)
>> + goto err;
>> +
>> + /* modulus */
>> + /* removing leading 0's */
>> + for (i = 0; i < rsa_key.n_sz && !rsa_key.n[i]; i++)
>> + ;
>> + (*prop)->num_bits = (rsa_key.n_sz - i) * 8;
>> + (*prop)->modulus = malloc(rsa_key.n_sz - i);
>> + if (!(*prop)->modulus) {
>> + ret = -ENOMEM;
>> + goto err;
>> + }
>> + memcpy((void *)(*prop)->modulus, &rsa_key.n[i], rsa_key.n_sz - i);
>> +
>> + /* exponent */
>> + (*prop)->public_exponent = calloc(1, sizeof(uint64_t));
>> + if (!(*prop)->public_exponent) {
>> + ret = -ENOMEM;
>> + goto err;
>> + }
>> + memcpy((void *)(*prop)->public_exponent + sizeof(uint64_t)
>> + - rsa_key.e_sz,
>> + rsa_key.e, rsa_key.e_sz);
>> + (*prop)->exp_len = rsa_key.e_sz;
>> +
>> + /* n0 inverse */
>> + br_i32_decode(n, &rsa_key.n[i], rsa_key.n_sz - i);
>> + (*prop)->n0inv = br_i32_ninv32(n[1]);
>> +
>> + /* R^2 mod n; R = 2^(num_bits) */
>> + rlen = (*prop)->num_bits * 2; /* #bits of R^2 = (2^num_bits)^2 */
>> + rr[0] = 0;
>> + *(uint8_t *)&rr[0] = (1 << (rlen % 8));
>> + for (i = 1; i < (((rlen + 31) >> 5) + 1); i++)
>> + rr[i] = 0;
>> + br_i32_decode(rrtmp, rr, ((rlen + 7) >> 3) + 1);
>> + br_i32_reduce(rr, rrtmp, n);
>> +
>> + rlen = ((*prop)->num_bits + 7) >> 3; /* #bytes of R^2 mod n */
>> + (*prop)->rr = malloc(rlen);
>> + if (!(*prop)->rr) {
>> + ret = -ENOMEM;
>> + goto err;
>> + }
>> + br_i32_encode((void *)(*prop)->rr, rlen, rr);
>> +
>> + return 0;
>> +
>> +err:
>> + free(n);
>> + free(rr);
>> + free(rrtmp);
>> + rsa_free_key_prop(*prop);
>> + return ret;
>> +}
>>
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