Fix a bug introduced in "Fix multiplication producing a negative zero" that
caused the sign to be forced to +1 when A > 0, B < 0 and B's low-order limb
is 0.
Add a non-regression test. More generally, systematically test combinations
of leading zeros, trailing zeros and signs.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
In mbedtls_mpi_read_string, if the string is empty, return an empty bignum
rather than a bignum with one limb with the value 0.
Both representations are correct, so this is not, in principle, a
user-visible change. The change does leak however through
mbedtls_mpi_write_string in base 16 (but not in other bases), as it writes a
bignum with 0 limbs as "" but a bignum with the value 0 and at least one
limb as "00".
This change makes it possible to construct an empty bignum through
mbedtls_mpi_read_string, which is especially useful to construct test
cases (a common use of mbedtls_mpi_read_string, as most formats use in
production encode numbers in binary, to be read with mbedtls_mpi_read_binary
or mbedtls_mpi_read_binary_le).
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Fix mbedtls_mpi_mul_mpi() when one of the operands is zero and the
other is negative. The sign of the result must be 1, since some
library functions do not treat {-1, 0, NULL} or {-1, n, {0}} as
representing the value 0.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Fix a null pointer dereference in mbedtls_mpi_exp_mod(X, A, N, E, _RR) when
A is the value 0 represented with 0 limbs.
Make the code a little more robust against similar bugs.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Test both 0 represented with 0 limbs ("0 (null)") and 0 represented
with 1 limb ("0 (1 limb)"), because occasionally there are bugs with
0-limb bignums and occasionally there are bugs with removing leading
zero limbs.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Remove the RR parameter to the mbedtls_mpi_exp_mod test function.
It was never used in the test data, so there is no loss of functionality.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Test mbedtls_mpi_safe_cond_assign() and mbedtls_mpi_safe_cond_swap()
with their "unsafe" counterparts mbedtls_mpi_copy() and
mbedtls_mpi_swap(). This way we don't need to repeat the coverage of
test cases.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Similarly to "Overhaul testing of mbedtls_mpi_copy", simplify the code
to test mbedtls_mpi_swap to have just one function for distinct MPIs
and one function for swapping an MPI with itself, covering all cases
of size (0, 1, >1) and sign (>0, <0).
The test cases are exactly the same as for mbedtls_mpi_copy with the
following replacements:
* `Copy` -> `Swap`
* ` to ` -> ` with `
* `_copy` -> `_swap`
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Replace the two test functions mbedtls_mpi_copy_sint (supporting signed
inputs but always with exactly one limb) and mbedtls_mpi_copy_binary
(supporting arbitrary-sized inputs but not negative inputs) by a single
function that supports both arbitrary-sized inputs and arbitrary-signed
inputs. This will allows testing combinations like negative source and
zero-sized destination.
Also generalize mpi_copy_self to support arbitrary inputs.
Generate a new list of test cases systematically enumerating all
possibilities among various categories: zero with 0 or 1 limb, negative or
positive with 1 limb, negative or positive with >1 limb. I used the
following Perl script:
```
sub rhs { $_ = $_[0]; s/bead/beef/; s/ca5cadedb01dfaceacc01ade/face1e55ca11ab1ecab005e5/; $_ }
%v = (
"zero (null)" => "",
"zero (1 limb)" => "0",
"small positive" => "bead",
"large positive" => "ca5cadedb01dfaceacc01ade",
"small negative" => "-bead",
"large negative" => "-ca5cadedb01dfaceacc01ade",
);
foreach $s (sort keys %v) {
foreach $d (sort keys %v) {
printf "Copy %s to %s\nmbedtls_mpi_copy:\"%s\":\"%s\"\n\n",
$s, $d, $v{$s}, rhs($v{$d});
}
}
foreach $s (sort keys %v) {
printf "Copy self: %s\nmpi_copy_self:\"%s\"\n\n", $s, $v{$s};
}
```
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Do more iterations with small values. This makes it more likely that a
mistake on bounds will be detected.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Add unit tests for mbedtls_mpi_fill_random() and mbedtls_mpi_random()
when the resulting MPI object previously had a nonzero value. I wrote
those to catch a bug that I introduced during the development of
mbedtls_mpi_random() (but does not appear in a committed version).
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
mbedtls_mpi_random() uses mbedtls_mpi_cmp_mpi_ct(), which requires its
two arguments to have the same storage size. This was not the case
when the upper bound passed to mbedtls_mpi_random() had leading zero
limbs.
Fix this by forcing the result MPI to the desired size. Since this is
not what mbedtls_mpi_fill_random() does, don't call it from
mbedtls_mpi_random(), but instead call a new auxiliary function.
Add tests to cover this and other conditions with varying sizes for
the two arguments.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Since mbedtls_mpi_random() is not specific to ECC code, move it from
the ECP module to the bignum module.
This increases the code size in builds without short Weierstrass
curves (including builds without ECC at all) that do not optimize out
unused functions.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Add test cases for mbedtls_mpi_sub_abs() where the second operand has
more limbs than the first operand (which, if the extra limbs are not
all zero, implies that the function returns
MBEDTLS_ERR_MPI_NEGATIVE_VALUE).
This exposes a buffer overflow (reported in #4042).
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Run all the addition and subtraction tests with the result aliased to
the first operand and with the result aliased to the second operand.
Before, only some of the aliasing possibilities were tested, for only
some of the functions, with only some inputs.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Fixes an issue where configs that had `MBEDTLS_MPI_MAX_BITS` greater than 256
but smaller than the test that was running (792 bits) the test would fail
incorrectly.
Signed-off-by: Chris Jones <christopher.jones@arm.com>
Move dependancy on `MBEDTLS_MPI_MAX_BITS` to apply to the specific test cases
which will break when `MBEDTLS_MPI_MAX_BITS` is too small. This re-enables
previous tests that were turned off accidentally.
Signed-off-by: Chris Jones <christopher.jones@arm.com>
In two test cases, the exponentiation computation was not being fully tested
as when A_bytes (the base) == N_bytes (the modulus) -> A = N. When this is the
case A is reduced to 0 and therefore the result of the computation will always
be 0.
This fixes that issue and therefore increases the test coverage to ensure
different computations are actually being run.
Signed-off-by: Chris Jones <christopher.jones@arm.com>
Reword test cases to be easier to read and understand.
Adds comments to better explain what the test is doing.
Signed-off-by: Chris Jones <christopher.jones@arm.com>
Add two further boundary tests for cases where both the exponent and modulus to
`mbedtls_mpi_exp_mod()` are `MBEDTLS_MPI_MAX_SIZE`, or longer, bytes long.
Signed-off-by: Chris Jones <christopher.jones@arm.com>
Adds test cases to ensure that `mbedtls_mpi_exp_mod` will return an error with
an exponent or modulus that is greater than `MBEDTLS_MPI_MAX_SIZE` in size.
Adds test cases to ensure that Diffie-Hellman will fail to make a key pair
(using `mbedtls_dhm_make_public`) when the prime modulus is greater than
`MBEDTLS_MPI_MAX_SIZE` in size.
Signed-off-by: Chris Jones <christopher.jones@arm.com>
Add a test case to ensure `mbedtls_mpi_exp_mod` fails when using a key size
larger than MBEDTLS_MPI_MAX_SIZE.
Add a test case to ensure that Diffie-Hellman operations fail when using a key
size larger than MBEDTLS_MPI_MAX_SIZE.
Signed-off-by: Chris Jones <christopher.jones@arm.com>
Positive tests: test that the RNG has the expected size, given that we
know how many leading zeros it has because we know how the function
consumes bytes and when the test RNG produces null bytes.
Negative tests: test that if the RNG is willing to emit less than the
number of wanted bytes, the function fails.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
The corner case tests were designed for 32 and 64 bit limbs
independently and performed only on the target platform. On the other
platform they are not corner cases anymore, but we can still exercise
them.
The corner case tests were designed for 64 bit limbs and failed on 32
bit platforms because the numbers in the test ended up being stored in a
different number of limbs and the function (correctly) returnd an error
upon receiving them.
The signature of mbedtls_mpi_cmp_mpi_ct() meant to support using it in
place of mbedtls_mpi_cmp_mpi(). This meant full comparison functionality
and a signed result.
To make the function more universal and friendly to constant time
coding, we change the result type to unsigned. Theoretically, we could
encode the comparison result in an unsigned value, but it would be less
intuitive.
Therefore we won't be able to represent the result as unsigned anymore
and the functionality will be constrained to checking if the first
operand is less than the second. This is sufficient to support the
current use case and to check any relationship between MPIs.
The only drawback is that we need to call the function twice when
checking for equality, but this can be optimised later if an when it is
needed.
