[openssl-users] ECC private key length

[Frode Nilsen]

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)
	priv:
	    77:76:fb:ae:7a:0b:97:98:aa:c0:70:7d:af:28:14:
	    6d:4f:03:d9:b5
	pub: 
	    04:9b:98:38:4a:d0:e4:22:a2:3f:80:ce:02:90:02:
	    d3:35:51:dc:8f:7b:5e:30:7d:2d:5e:98:6f:4b:9b:
	    4b:c8:01:1c:2d:ce:39:37:04:c5:61
	ASN1 OID: secp160k1

However, following "priv:", there are only 20 bytes (160 bits). Why is this?

When printing the keypair for other curves, the number of bytes after "priv:" seem to always be the same or higher than the number of bits shown after "Private-Key:".

Thanks in advance,
Frode