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Contextualize comment about mbedtls_mpi_random retries

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This comment is no longer in the specific context of generating a
random point on an elliptic curve.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-04-13 19:59:21 +02:00
parent 3b05615e5b
commit ef1325134f
1 changed files with 5 additions and 3 deletions
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8
library/bignum.c
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@ -2498,9 +2498,11 @@ int mbedtls_mpi_random( mbedtls_mpi *X,
* a probability 1/2 of being 0, and then the result will be < N), * a probability 1/2 of being 0, and then the result will be < N),
* so after 30 tries failure probability is a most 2**(-30). * so after 30 tries failure probability is a most 2**(-30).
* *
* For most curves, 1 try is enough with overwhelming probability, * When N is just below a power of 2, as is the case when generating
* since N starts with a lot of 1s in binary, but some curves * a random point on most elliptic curves, 1 try is enough with
* such as secp224k1 are actually very close to the worst case. * overwhelming probability. When N is just above a power of 2,
* as when generating a random point on secp224k1, each try has
* a probability of failing that is almost 1/2.
*/ */
if( ++count > 30 ) if( ++count > 30 )
{ {