On 15/04/12 23:33, Dr. Stephen Henson wrote:
On Sun, Apr 15, 2012, Jeffrey Walton wrote:
On Sun, Apr 15, 2012 at 12:01 PM,<toredhiddenu...@tormail.net> wrote:
Hello guyz and cryptobrains! :P
One of the main disadvantages of EC on openssl seems to be the inability
to create arbitrary-sized keys and advantage for RSA: you can create 32768
bit RSA key but... not greater than 521 bits on ECC.
Will this continue to be a disadvantage or can 32768 RSA key be used instead?
Point counting is tricky business. I believe it is the reason most
folks (OpenSSL, Crypto++, NSS, etc) stick with well known curves.
I don't know how to plug in a custom curve with OpenSSL (I have never
had a need to do it), but I do know how with Crypto++. If I wanted to
do so, I would use Marcel Martin's Elliptic Curve Builder (ECB) to
generate domain parameters to meet security levels.
It should be possible to use a non-named curve with the appropriate encoding
of the ECParameters structure. I've never had to do this either.
The library only supports Fp and F2^m custom curves. The easiest way to
construct a custom curve is by using one of:
EC_GROUP *EC_GROUP_new_curve_GFp(const BIGNUM *p, const BIGNUM *a, const
BIGNUM *b, BN_CTX *ctx);
EC_GROUP *EC_GROUP_new_curve_GF2m(const BIGNUM *p, const BIGNUM *a, const
BIGNUM *b, BN_CTX *ctx);
Where for an Fp curve p, a and b are used as follows:
y^2 mod p = x^3 +ax + b mod p
And for an F2^m curve p (p=2^m), a and b are:
y^2 + xy mod p = x^3 + ax^2 + b (where b != 0) mod p
Matt
Steve.
--
Dr Stephen N. Henson. OpenSSL project core developer.
Commercial tech support now available see: http://www.openssl.org
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