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Fix potential DoS by limiting number sizes in exponentiation

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Check that the exponent and modulus is below `MBEDTLS_MPI_MAX_BITS` before
performing a time expensive operation (modular exponentiation). This prevents
a potential DoS from Diffie-Hellman computations with extremely
large key sizes.

Signed-off-by: Chris Jones <christopher.jones@arm.com>
This commit is contained in:
Chris Jones 2020-11-25 15:12:39 +00:00
parent 4685d501e8
commit 8b1f65ea00
1 changed files with 4 additions and 0 deletions
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4
library/bignum.c
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@ -1859,6 +1859,10 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A, const mbedtls_mpi
if( mbedtls_mpi_cmp_int( E, 0 ) < 0 )
return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
if( mbedtls_mpi_bitlen( E ) > MBEDTLS_MPI_MAX_BITS ||
mbedtls_mpi_bitlen( N ) > MBEDTLS_MPI_MAX_BITS )
return ( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
/*
* Init temps and window size
*/