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Fix mbedtls_pk_get_bitlen() for RSA with non-byte-aligned sizes

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Add non-regression tests. Update some test functions to not assume that
byte_length == bit_length / 8.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine
2024-02-01 22:33:06 +01:00
parent ede909f99a
commit 0196f4886a
6 changed files with 65 additions and 6 deletions
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18
library/pk_wrap.c
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@ -53,7 +53,23 @@ static int rsa_can_do(mbedtls_pk_type_t type)
static size_t rsa_get_bitlen(const void *ctx)
{
const mbedtls_rsa_context *rsa = (const mbedtls_rsa_context *) ctx;
return 8 * mbedtls_rsa_get_len(rsa);
/* Unfortunately, the rsa.h interface does not have a direct way
* to access the bit-length that works with MBEDTLS_RSA_ALT.
* So we have to do a little work here.
*/
mbedtls_mpi N;
mbedtls_mpi_init(&N);
int ret = mbedtls_rsa_export(rsa, &N, NULL, NULL, NULL, NULL);
/* If the export fails for some reason (e.g. the RSA_ALT implementation
* does not support export, or there is not enough memory),
* we have no way of returning an error from this function.
* As a fallback, return the byte-length converted in bits, which is
* the correct value if the modulus size is a multiple of 8 bits, which
* is very often the case in practice. */
size_t bitlen = (ret == 0 ? mbedtls_mpi_bitlen(&N) :
8 * mbedtls_rsa_get_len(rsa));
mbedtls_mpi_free(&N);
return bitlen;
}
static int rsa_verify_wrap(void *ctx, mbedtls_md_type_t md_alg,