2023-06-13 16:20:21

by Mahmoud Adam

Subject: [PATCH] crypto: rsa - allow only odd e and restrict value in FIPS mode

check if rsa public exponent is odd and check its value is between
2^16 < e < 2^256.

FIPS 186-5 DSS (page 35)[1] specify that:
1. The public exponent e shall be selected with the following constraints:
(a) The public verification exponent e shall be selected prior to
generating the primes, p and q, and the private signature exponent
d.
(b) The exponent e shall be an odd positive integer such that:
2^16 < e < 2^256.

[1] https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-5.pdf

Signed-off-by: Mahmoud Adam <[email protected]>
---
crypto/rsa.c | 36 ++++++++++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)

diff --git a/crypto/rsa.c b/crypto/rsa.c
index c50f2d2a4d06..c79613cdce6e 100644
--- a/crypto/rsa.c
+++ b/crypto/rsa.c
@@ -205,6 +205,32 @@ static int rsa_check_key_length(unsigned int len)
return -EINVAL;
}

+static int rsa_check_exponent_fips(MPI e)
+{
+ MPI e_max = NULL;
+
+ /* check if odd */
+ if (!mpi_test_bit(e, 0)) {
+ return -EINVAL;
+ }
+
+ /* check if 2^16 < e < 2^256. */
+ if (mpi_cmp_ui(e, 65536) <= 0) {
+ return -EINVAL;
+ }
+
+ e_max = mpi_alloc(0);
+ mpi_set_bit(e_max, 256);
+
+ if (mpi_cmp(e, e_max) >= 0) {
+ mpi_free(e_max);
+ return -EINVAL;
+ }
+
+ mpi_free(e_max);
+ return 0;
+}
+
static int rsa_set_pub_key(struct crypto_akcipher *tfm, const void *key,
unsigned int keylen)
{
@@ -232,6 +258,11 @@ static int rsa_set_pub_key(struct crypto_akcipher *tfm, const void *key,
return -EINVAL;
}

+ if (fips_enabled && rsa_check_exponent_fips(mpi_key->e)) {
+ rsa_free_mpi_key(mpi_key);
+ return -EINVAL;
+ }
+
return 0;

err:
@@ -290,6 +321,11 @@ static int rsa_set_priv_key(struct crypto_akcipher *tfm, const void *key,
return -EINVAL;
}

+ if (fips_enabled && rsa_check_exponent_fips(mpi_key->e)) {
+ rsa_free_mpi_key(mpi_key);
+ return -EINVAL;
+ }
+
return 0;

err:
--
2.40.1

2023-06-14 09:57:04

by Herbert Xu

Subject: Re: [PATCH] crypto: rsa - allow only odd e and restrict value in FIPS mode

On Tue, Jun 13, 2023 at 04:17:31PM +0000, Mahmoud Adam wrote:
> check if rsa public exponent is odd and check its value is between
> 2^16 < e < 2^256.
>
> FIPS 186-5 DSS (page 35)[1] specify that:
> 1. The public exponent e shall be selected with the following constraints:
> (a) The public verification exponent e shall be selected prior to
> generating the primes, p and q, and the private signature exponent
> d.
> (b) The exponent e shall be an odd positive integer such that:
> 2^16 < e < 2^256.
>
> [1] https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-5.pdf
>
> Signed-off-by: Mahmoud Adam <[email protected]>
> ---
> crypto/rsa.c | 36 ++++++++++++++++++++++++++++++++++++
> 1 file changed, 36 insertions(+)
>
> diff --git a/crypto/rsa.c b/crypto/rsa.c
> index c50f2d2a4d06..c79613cdce6e 100644
> --- a/crypto/rsa.c
> +++ b/crypto/rsa.c
> @@ -205,6 +205,32 @@ static int rsa_check_key_length(unsigned int len)
> return -EINVAL;
> }
>
> +static int rsa_check_exponent_fips(MPI e)
> +{
> + MPI e_max = NULL;
> +
> + /* check if odd */
> + if (!mpi_test_bit(e, 0)) {
> + return -EINVAL;
> + }
> +
> + /* check if 2^16 < e < 2^256. */
> + if (mpi_cmp_ui(e, 65536) <= 0) {
> + return -EINVAL;
> + }
> +
> + e_max = mpi_alloc(0);
> + mpi_set_bit(e_max, 256);
> +
> + if (mpi_cmp(e, e_max) >= 0) {
> + mpi_free(e_max);
> + return -EINVAL;
> + }
> +
> + mpi_free(e_max);
> + return 0;
> +}
> +
> static int rsa_set_pub_key(struct crypto_akcipher *tfm, const void *key,
> unsigned int keylen)
> {
> @@ -232,6 +258,11 @@ static int rsa_set_pub_key(struct crypto_akcipher *tfm, const void *key,
> return -EINVAL;
> }
>
> + if (fips_enabled && rsa_check_exponent_fips(mpi_key->e)) {
> + rsa_free_mpi_key(mpi_key);
> + return -EINVAL;
> + }
> +
> return 0;
>
> err:
> @@ -290,6 +321,11 @@ static int rsa_set_priv_key(struct crypto_akcipher *tfm, const void *key,
> return -EINVAL;
> }
>
> + if (fips_enabled && rsa_check_exponent_fips(mpi_key->e)) {
> + rsa_free_mpi_key(mpi_key);
> + return -EINVAL;
> + }
> +
> return 0;
>
> err:
> --
> 2.40.1

Cc Stephan Mueller
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

2023-06-14 12:02:55

by Stephan Müller

Subject: Re: [PATCH] crypto: rsa - allow only odd e and restrict value in FIPS mode

Am Mittwoch, 14. Juni 2023, 11:50:52 CEST schrieb Herbert Xu:

Hi Herbert,

> On Tue, Jun 13, 2023 at 04:17:31PM +0000, Mahmoud Adam wrote:
> > check if rsa public exponent is odd and check its value is between
> > 2^16 < e < 2^256.
> >
> > FIPS 186-5 DSS (page 35)[1] specify that:
> >
> > 1. The public exponent e shall be selected with the following constraints:
> > (a) The public verification exponent e shall be selected prior to
> > generating the primes, p and q, and the private signature exponent
> > d.
> >
> > (b) The exponent e shall be an odd positive integer such that:
> > 2^16 < e < 2^256.
> >
> > [1] https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-5.pdf
> >
> > Signed-off-by: Mahmoud Adam <[email protected]>

Reviewed-by: Stephan Mueller <[email protected]>

Ciao
Stephan