Some keys work, some fail about picotls HOT 2 CLOSED

I believe that the particular version of OpenSSL you are using is prepending 00 when the most-significant bit of the private key is set, as you need to do for ASN.1.

Interestingly, whether if such padding is made seems to depend on the version of the OpenSSL; as shown below, OpenSSL 1.1.0 does not prepend 00 to the output.

$ /usr/local/openssl-1.0.2/bin/openssl ec -in key.pem -text
read EC key
Private-Key: (256 bit)
priv:
    00:fe:44:a5:6f:e8:18:a6:b6:28:6a:5a:e1:a6:86:
    3c:02:4e:42:50:77:90:4e:d2:dc:89:99:c5:24:2e:
    a3:9e:77
pub: 
(snip)
$ /usr/local/openssl-1.1.0/bin/openssl ec -in key.pem -text
read EC key
Private-Key: (256 bit)
priv:
    fe:44:a5:6f:e8:18:a6:b6:28:6a:5a:e1:a6:86:3c:
    02:4e:42:50:77:90:4e:d2:dc:89:99:c5:24:2e:a3:
    9e:77
pub:
(snip)

Considering the facts, I'd suggest removing the first byte on the script side if the length of the private key is 1 byte longer than expected and if the first byte is 00.

from picotls.

Thanks! I fixed this in NTAP/quant@dc414c9

from picotls.