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| author | Nicola Tuveri <nic.tuv@gmail.com> | 2019-11-12 00:52:00 +0200 |
|---|---|---|
| committer | Nicola Tuveri <nic.tuv@gmail.com> | 2019-11-13 18:02:51 +0200 |
| commit | 3cc26f2eba8a8c16ac559e68c05c094d7ea6bd8b (patch) | |
| tree | 4556378c60968fb26d06a618caea4de11a123977 /doc | |
| parent | 35ed029b5a488924890fda2487c87f664361a33b (diff) | |
Extend docs for EC_POINT conversion functions
Add more explicit documentation about the relation between
EC_POINT_point2oct(), EC_POINT_point2hex(), EC_POINT_point2bn() and
their reverse.
In particular highlight that EC_POINT_point2oct() and
EC_POINT_oct2point() conform to, respectively, Sec. 2.3.3 and Sec. 2.3.4
of the SECG SEC 1 standard (which is the normative reference for the
already mentioned RFC 5480), highlighting with a note how this affect
the encoding/decoding of the point at infinity (which in contrast with
any other valid generic point of a curve is assigned an exceptional
fixed octet string encoding, i.e., 0x00).
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/10329)
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/man3/EC_POINT_new.pod | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/doc/man3/EC_POINT_new.pod b/doc/man3/EC_POINT_new.pod index 42eaddd460..f941446fd5 100644 --- a/doc/man3/EC_POINT_new.pod +++ b/doc/man3/EC_POINT_new.pod @@ -171,6 +171,26 @@ The functions EC_POINT_point2oct(), EC_POINT_oct2point(), EC_POINT_point2bn(), EC_POINT_bn2point(), EC_POINT_point2hex() and EC_POINT_hex2point() convert from and to EC_POINTs for the formats: octet, BIGNUM and hexadecimal respectively. +The function EC_POINT_point2oct() encodes the given curve point B<p> as an +octet string into the buffer B<buf> of size B<len>, using the specified +conversion form B<form>. +The encoding conforms with Sec. 2.3.3 of the SECG SEC 1 ("Elliptic Curve +Cryptography") standard. +Similarly the function EC_POINT_oct2point() decodes a curve point into B<p> from +the octet string contained in the given buffer B<buf> of size B<len>, conforming +to Sec. 2.3.4 of the SECG SEC 1 ("Elliptic Curve Cryptography") standard. + +The functions EC_POINT_point2hex() and EC_POINT_point2bn() convert a point B<p>, +respectively, to the hexadecimal or BIGNUM representation of the same +encoding of the function EC_POINT_point2oct(). +Vice versa, similarly to the function EC_POINT_oct2point(), the functions +EC_POINT_hex2point() and EC_POINT_point2bn() decode the hexadecimal or +BIGNUM representation into the EC_POINT B<p>. + +Notice that, according to the standard, the octet string encoding of the point +at infinity for a given curve is fixed to a single octet of value zero and that, +vice versa, a single octet of size zero is decoded as the point at infinity. + The function EC_POINT_point2oct() must be supplied with a buffer long enough to store the octet form. The return value provides the number of octets stored. Calling the function with a NULL buffer will not perform the conversion but |