rsa.c

Go to the documentation of this file.

#include "includes.h"

#include "common.h"
#include "crypto.h"
#include "asn1.h"
#include "bignum.h"
#include "rsa.h"


struct crypto_rsa_key {
        int private_key; /* whether private key is set */
        struct bignum *n; /* modulus (p * q) */
        struct bignum *e; /* public exponent */
        /* The following parameters are available only if private_key is set */
        struct bignum *d; /* private exponent */
        struct bignum *p; /* prime p (factor of n) */
        struct bignum *q; /* prime q (factor of n) */
        struct bignum *dmp1; /* d mod (p - 1); CRT exponent */
        struct bignum *dmq1; /* d mod (q - 1); CRT exponent */
        struct bignum *iqmp; /* 1 / q mod p; CRT coefficient */
};


static const u8 * crypto_rsa_parse_integer(const u8 *pos, const u8 *end,
                                           struct bignum *num)
{
        struct asn1_hdr hdr;

        if (pos == NULL)
                return NULL;

        if (asn1_get_next(pos, end - pos, &hdr) < 0 ||
            hdr.class != ASN1_CLASS_UNIVERSAL || hdr.tag != ASN1_TAG_INTEGER) {
                wpa_printf(MSG_DEBUG, "RSA: Expected INTEGER - found class %d "
                           "tag 0x%x", hdr.class, hdr.tag);
                return NULL;
        }

        if (bignum_set_unsigned_bin(num, hdr.payload, hdr.length) < 0) {
                wpa_printf(MSG_DEBUG, "RSA: Failed to parse INTEGER");
                return NULL;
        }

        return hdr.payload + hdr.length;
}


struct crypto_rsa_key *
crypto_rsa_import_public_key(const u8 *buf, size_t len)
{
        struct crypto_rsa_key *key;
        struct asn1_hdr hdr;
        const u8 *pos, *end;

        key = os_zalloc(sizeof(*key));
        if (key == NULL)
                return NULL;

        key->n = bignum_init();
        key->e = bignum_init();
        if (key->n == NULL || key->e == NULL) {
                crypto_rsa_free(key);
                return NULL;
        }

        /*
         * PKCS #1, 7.1:
         * RSAPublicKey ::= SEQUENCE {
         *     modulus INTEGER, -- n
         *     publicExponent INTEGER -- e 
         * }
         */

        if (asn1_get_next(buf, len, &hdr) < 0 ||
            hdr.class != ASN1_CLASS_UNIVERSAL ||
            hdr.tag != ASN1_TAG_SEQUENCE) {
                wpa_printf(MSG_DEBUG, "RSA: Expected SEQUENCE "
                           "(public key) - found class %d tag 0x%x",
                           hdr.class, hdr.tag);
                goto error;
        }
        pos = hdr.payload;
        end = pos + hdr.length;

        pos = crypto_rsa_parse_integer(pos, end, key->n);
        pos = crypto_rsa_parse_integer(pos, end, key->e);

        if (pos == NULL)
                goto error;

        if (pos != end) {
                wpa_hexdump(MSG_DEBUG,
                            "RSA: Extra data in public key SEQUENCE",
                            pos, end - pos);
                goto error;
        }

        return key;

error:
        crypto_rsa_free(key);
        return NULL;
}


struct crypto_rsa_key *
crypto_rsa_import_private_key(const u8 *buf, size_t len)
{
        struct crypto_rsa_key *key;
        struct bignum *zero;
        struct asn1_hdr hdr;
        const u8 *pos, *end;

        key = os_zalloc(sizeof(*key));
        if (key == NULL)
                return NULL;

        key->private_key = 1;

        key->n = bignum_init();
        key->e = bignum_init();
        key->d = bignum_init();
        key->p = bignum_init();
        key->q = bignum_init();
        key->dmp1 = bignum_init();
        key->dmq1 = bignum_init();
        key->iqmp = bignum_init();

        if (key->n == NULL || key->e == NULL || key->d == NULL ||
            key->p == NULL || key->q == NULL || key->dmp1 == NULL ||
            key->dmq1 == NULL || key->iqmp == NULL) {
                crypto_rsa_free(key);
                return NULL;
        }

        /*
         * PKCS #1, 7.2:
         * RSAPrivateKey ::= SEQUENCE {
         *    version Version,
         *    modulus INTEGER, -- n
         *    publicExponent INTEGER, -- e
         *    privateExponent INTEGER, -- d
         *    prime1 INTEGER, -- p
         *    prime2 INTEGER, -- q
         *    exponent1 INTEGER, -- d mod (p-1)
         *    exponent2 INTEGER, -- d mod (q-1)
         *    coefficient INTEGER -- (inverse of q) mod p
         * }
         *
         * Version ::= INTEGER -- shall be 0 for this version of the standard
         */
        if (asn1_get_next(buf, len, &hdr) < 0 ||
            hdr.class != ASN1_CLASS_UNIVERSAL ||
            hdr.tag != ASN1_TAG_SEQUENCE) {
                wpa_printf(MSG_DEBUG, "RSA: Expected SEQUENCE "
                           "(public key) - found class %d tag 0x%x",
                           hdr.class, hdr.tag);
                goto error;
        }
        pos = hdr.payload;
        end = pos + hdr.length;

        zero = bignum_init();
        if (zero == NULL)
                goto error;
        pos = crypto_rsa_parse_integer(pos, end, zero);
        if (pos == NULL || bignum_cmp_d(zero, 0) != 0) {
                wpa_printf(MSG_DEBUG, "RSA: Expected zero INTEGER in the "
                           "beginning of private key; not found");
                bignum_deinit(zero);
                goto error;
        }
        bignum_deinit(zero);

        pos = crypto_rsa_parse_integer(pos, end, key->n);
        pos = crypto_rsa_parse_integer(pos, end, key->e);
        pos = crypto_rsa_parse_integer(pos, end, key->d);
        pos = crypto_rsa_parse_integer(pos, end, key->p);
        pos = crypto_rsa_parse_integer(pos, end, key->q);
        pos = crypto_rsa_parse_integer(pos, end, key->dmp1);
        pos = crypto_rsa_parse_integer(pos, end, key->dmq1);
        pos = crypto_rsa_parse_integer(pos, end, key->iqmp);

        if (pos == NULL)
                goto error;

        if (pos != end) {
                wpa_hexdump(MSG_DEBUG,
                            "RSA: Extra data in public key SEQUENCE",
                            pos, end - pos);
                goto error;
        }

        return key;

error:
        crypto_rsa_free(key);
        return NULL;
}


size_t crypto_rsa_get_modulus_len(struct crypto_rsa_key *key)
{
        return bignum_get_unsigned_bin_len(key->n);
}


int crypto_rsa_exptmod(const u8 *in, size_t inlen, u8 *out, size_t *outlen,
                       struct crypto_rsa_key *key, int use_private)
{
        struct bignum *tmp, *a = NULL, *b = NULL;
        int ret = -1;
        size_t modlen;

        if (use_private && !key->private_key)
                return -1;

        tmp = bignum_init();
        if (tmp == NULL)
                return -1;

        if (bignum_set_unsigned_bin(tmp, in, inlen) < 0)
                goto error;
        if (bignum_cmp(key->n, tmp) < 0) {
                /* Too large input value for the RSA key modulus */
                goto error;
        }

        if (use_private) {
                /*
                 * Decrypt (or sign) using Chinese remainer theorem to speed
                 * up calculation. This is equivalent to tmp = tmp^d mod n
                 * (which would require more CPU to calculate directly).
                 *
                 * dmp1 = (1/e) mod (p-1)
                 * dmq1 = (1/e) mod (q-1)
                 * iqmp = (1/q) mod p, where p > q
                 * m1 = c^dmp1 mod p
                 * m2 = c^dmq1 mod q
                 * h = q^-1 (m1 - m2) mod p
                 * m = m2 + hq
                 */
                a = bignum_init();
                b = bignum_init();
                if (a == NULL || b == NULL)
                        goto error;

                /* a = tmp^dmp1 mod p */
                if (bignum_exptmod(tmp, key->dmp1, key->p, a) < 0)
                        goto error;

                /* b = tmp^dmq1 mod q */
                if (bignum_exptmod(tmp, key->dmq1, key->q, b) < 0)
                        goto error;

                /* tmp = (a - b) * (1/q mod p) (mod p) */
                if (bignum_sub(a, b, tmp) < 0 ||
                    bignum_mulmod(tmp, key->iqmp, key->p, tmp) < 0)
                        goto error;

                /* tmp = b + q * tmp */
                if (bignum_mul(tmp, key->q, tmp) < 0 ||
                    bignum_add(tmp, b, tmp) < 0)
                        goto error;
        } else {
                /* Encrypt (or verify signature) */
                /* tmp = tmp^e mod N */
                if (bignum_exptmod(tmp, key->e, key->n, tmp) < 0)
                        goto error;
        }

        modlen = crypto_rsa_get_modulus_len(key);
        if (modlen > *outlen) {
                *outlen = modlen;
                goto error;
        }

        if (bignum_get_unsigned_bin_len(tmp) > modlen)
                goto error; /* should never happen */

        *outlen = modlen;
        os_memset(out, 0, modlen);
        if (bignum_get_unsigned_bin(
                    tmp, out +
                    (modlen - bignum_get_unsigned_bin_len(tmp)), NULL) < 0)
                goto error;

        ret = 0;

error:
        bignum_deinit(tmp);
        bignum_deinit(a);
        bignum_deinit(b);
        return ret;
}


void crypto_rsa_free(struct crypto_rsa_key *key)
{
        if (key) {
                bignum_deinit(key->n);
                bignum_deinit(key->e);
                bignum_deinit(key->d);
                bignum_deinit(key->p);
                bignum_deinit(key->q);
                bignum_deinit(key->dmp1);
                bignum_deinit(key->dmq1);
                bignum_deinit(key->iqmp);
                os_free(key);
        }
}

---