Call to EC_POINT_set_compressed_coodinates() with with x-coordinate and
y-bit will resolve the curve equation for y and chooses y out of two
possible y values based on y-bit input.
You can retrieve the x and y co-ordinates using
EC_POINT_get_affine_coordinates as below, where x-cordinate matches w
I checked the 'test' folder but I didn't found any tests that help me
in this case.
However the only doubt is how I can use the API offered by openssl library.
I understand how retreive a point (and consequently to assign it to a
public key) starting from a compressed-y representation (which
> If I have an x-point which follows this representation
> https://tools.ietf.org/id/draft-jivsov-ecc-compact-05.html (so it is
> composed by 33 byte and first byte is '0x02') and I use
> 'EC_POINT_set_compressed_coordinates_GFp' function, it will be
> considered as compressed-y-0 or compressed-y-1
But the y bit is indicated by the foutth parameter of
'EC_POINT_set_compressed_coordinates_GFp' function.
Isn't the representation you linked different by that that I linked
previously?
Luca
Thulasi Goriparthi ha scritto:
02 indicates y bit is 0
03 indicates y bit is 1
http://citeseerx.i
02 indicates y bit is 0
03 indicates y bit is 1
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.202.2977&rep=rep1&type=pdf
Thanks,
Thulasi.
On Fri, 25 Oct 2019 at 16:50, Luca Di Mauro wrote:
>
> Mh, maybe I didn't understand.
>
> If I have an x-point which follows this representation
Mh, maybe I didn't understand.
If I have an x-point which follows this representation
https://tools.ietf.org/id/draft-jivsov-ecc-compact-05.html (so it is
composed by 33 byte and first byte is '0x02') and I use
'EC_POINT_set_compressed_coordinates_GFp' function, it will be
considered as
> Thank you! I thought they were the same.
>
> And given an x-only coordinate, how can I find the y coordinate? I
> don't find the relative functions on the documentation.
Well it depends on what you mean. Internally,
EC_POINT_set_compressed_coordinates_GFp will internally automatically
compute th
Thank you! I thought they were the same.
And given an x-only coordinate, how can I find the y coordinate? I
don't find the relative functions on the documentation.
Luca
Billy Brumley ha scritto:
Don't do that. As I said, the library is trying to tell you that's not a
point on the secp256k
Don't do that. As I said, the library is trying to tell you that's not a
point on the secp256k1 curve.
Quickly browsing the standard, you are likely looking for the prime256v1
curve.
BBB
On Fri, 25 Oct 2019, 9.28 Luca Di Mauro, wrote:
> I think it is correct because I extracted the hexadecimal
I think it is correct because I extracted the hexadecimal string from
a packet contained in a pcap.
This compressed point is created following the ETSI TS 103 097 v1.3.1
standard for secured communications in the vehicular communication
context
(https://www.etsi.org/deliver/etsi_ts/103000
> EC_GROUP* group = EC_GROUP_new_by_curve_name (NID_secp256k1);
> "c16b4ce0532f5dc9d09114fe121d3956ae84f9eb677a0d4bdac1d3af7a91950c";
I don't believe there's a point on secp256k1 with that x-coordinate.
If you check the failure reason for
EC_POINT_set_compressed_coordinates_GFp in
Hi,
the link you posted below are very useful!
However, after many trials and errors, I created a little program to
derive a public key from an x-only coordinate but, in the last step,
it fails, namely in the function
'EC_POINT_set_compressed_coordinates_GFp' called in the function
'loadK
Thank you very much for the reply!
Yes, I have also the additional information about on which of two
solutions I should take.
I'll check the guides you linked below.
Luca Di Mauro
Nicola Tuveri ha scritto:
Hi,
with traditional EC from the x coordinate alone you can't really do that,
beca
Hi,
with traditional EC from the x coordinate alone you can't really do that,
because there are always 2 possible solutions for y (in R the curve is
symmetrical on the x axis).
The standards define a "compressed point" format in which you can send the
coordinate x and an additional bit to select
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