libgcrypt: Elliptic Curve Points Compact Representation

Yann Garcia yann.garcia at
Mon Nov 5 12:07:37 CET 2018

Dear All,

I'm currently developing a Wireshark dissector for protocols based on IEEE
1609.2 standard.
This standard uses extensively the canonical form which is defined by using
compact representation of public x,y keys.

My trouble is how can I retrieve the private and uncompressed public keys
when only the y key sign (LSB bit is 0 or 1) and the x public key is

NOTE: The Nist P-256 ECC curve is used.

Please may I ask you some hints to address my trouble?

Many thanks in advance for your help,

Best regards,

Yann Garcia
Senior Software Engineer
Microsoft Certified
Le Montespan B2
  Avenue des Alpes
F-06600 Antibes, FRANCE
Tel: +33 (0)4 92 94 49 08
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Email: *yann.garcia at <yann.garcia at>*
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