Fix potential DoS by limiting number sizes in exponentiation
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>
diff --git a/library/bignum.c b/library/bignum.c
index 3135ec4..ba4bb83 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1859,6 +1859,10 @@
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
*/