[Gnuk-users] RSA-4096 and ECC

[NIIBE Yutaka]

In the rsa_4096_support branch (of git.gniibe.org), support
of RSA-4096 is added.

It is added along with ECC NIST P256, ECC SEC P256K1 (it's famous by
Bitcoin), and Ed25519.

I only tested RSA-4096 (sign and decrypt).  It takes more than 8.7
second.

Because memory is tight, we can't have large window size for
computation of exponentiation.  For 2048-bit, window size is 6, and we
take advantage of using precomputed table, but it's only 4 for
4096-bit (table became too large if it were 6).  The function
implementation in question is:
	gnuk/polarssl/library/bignum.c:mpi_exp_mod

I haven't tested keygeneration, which might require more change,
possibly.  All existing tests (for RSA-2048) go well.

I'm going to test/check other kinds of keys.  I don't know if
NIST P256 could be useful, but Ed25519 will be surely useful.
For SEC P256K1, I don't know.
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