It's because of the form of the group order for the curves you list.
They look roughly like 2**n + 2**(n/2). So while technically possible
to end up with 161 bits, with overwhelming probability you end up with
less.
BBB
On Wed, Apr 6, 2016 at 9:22 PM, Frode Nilsen wrote:
> Hi,
>
> When printing
Hi,
When printing the contents of a PEM ECC keypair file for the secp160k1/r1/r2
curves, OpenSSL says the private key is 161 bits:
$ openssl ecparam -name secp160k1 -genkey -out test.pem
$ openssl ec -in test.pem -text -noout
read EC key
Private-Key: (161 bit)
