Re: [Dcrup] Hey, crypto experts, what signing algorithm should we add

["Mark D. Baushke" <[e-mail]>]

For OpenSSL and ECDSA, the following example may help you:

$ openssl version
OpenSSL 1.0.2l  25 May 2017
$ : Tell OpenSSL what Elliptic Curve you want to use: prime256v1 in this case
$ openssl ecparam -out prime256v1-param.pem -name prime256v1
$ cat prime256v1-param.pem
-----BEGIN EC PARAMETERS-----
BggqhkjOPQMBBw==
-----END EC PARAMETERS-----
$ : Generate a private key based on the prime256v1
$ openssl ecparam -in prime256v1-param.pem -genkey -out my_privatekey.pem
$ cat my_privatekey.pem
-----BEGIN EC PARAMETERS-----
BggqhkjOPQMBBw==
-----END EC PARAMETERS-----
-----BEGIN EC PRIVATE KEY-----
MHcCAQEEIEwjT+3tXgsoPmQ4dGnVtAzuC03S7HHRiqPxifL0cE8UoAoGCCqGSM49
AwEHoUQDQgAEFTtSp6kPe2fjNNfHiaKGpMYFs19xnj6hTfpdmklxE1Y1ERP2Zlgj
2QG5vSbb13xbQ+EPcMdoLt4lBTpy+wxDQw==
-----END EC PRIVATE KEY-----
$ openssl ec -in my_privatekey.pem -noout -text
read EC key
Private-Key: (256 bit)
priv:
    4c:23:4f:ed:ed:5e:0b:28:3e:64:38:74:69:d5:b4:
    0c:ee:0b:4d:d2:ec:71:d1:8a:a3:f1:89:f2:f4:70:
    4f:14
pub:
    04:15:3b:52:a7:a9:0f:7b:67:e3:34:d7:c7:89:a2:
    86:a4:c6:05:b3:5f:71:9e:3e:a1:4d:fa:5d:9a:49:
    71:13:56:35:11:13:f6:66:58:23:d9:01:b9:bd:26:
    db:d7:7c:5b:43:e1:0f:70:c7:68:2e:de:25:05:3a:
    72:fb:0c:43:43
ASN1 OID: prime256v1
NIST CURVE: P-256
$ : Generate public key
$ openssl ec -in my_privatekey.pem -pubout -out my_publickey.pem
read EC key
writing EC key
$ cat my_publickey.pem
-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEFTtSp6kPe2fjNNfHiaKGpMYFs19x
nj6hTfpdmklxE1Y1ERP2Zlgj2QG5vSbb13xbQ+EPcMdoLt4lBTpy+wxDQw==
-----END PUBLIC KEY-----
$ 

If you look the PEM file contains the following prefix before the "pub:"
key

$ openssl ec -in my_privatekey.pem -pubout -out my_publickey.der -outform der
read EC key
writing EC key
$ od -t x1 my_publickey.der
0000000    30  59  30  13  06  07  2a  86  48  ce  3d  02  01  06  08  2a
0000020    86  48  ce  3d  03  01  07  03  42  00  04  15  3b  52  a7  a9
0000040    0f  7b  67  e3  34  d7  c7  89  a2  86  a4  c6  05  b3  5f  71
0000060    9e  3e  a1  4d  fa  5d  9a  49  71  13  56  35  11  13  f6  66
0000100    58  23  d9  01  b9  bd  26  db  d7  7c  5b  43  e1  0f  70  c7
0000120    68  2e  de  25  05  3a  72  fb  0c  43  43
$

Which decomposes to some front material:

    30:59:30:13:06:07:2a:86:48:ce:3d:02:01:06:08:2a:
    86:48:ce:3d:03:01:07:03:42:00:

followed by the public key:

    04:15:3b:52:a7:a9:0f:7b:67:e3:34:d7:c7:89:a2:
    86:a4:c6:05:b3:5f:71:9e:3e:a1:4d:fa:5d:9a:49:
    71:13:56:35:11:13:f6:66:58:23:d9:01:b9:bd:26:
    db:d7:7c:5b:43:e1:0f:70:c7:68:2e:de:25:05:3a:
    72:fb:0c:43:43


Use the key...

$ echo hello world > hello.txt
$ openssl dgst -sha256 -sign my_privatekey.pem hello.txt > hello.sig
$ openssl dgst -sha256 -verify my_publickey.pem -signature hello.sig hello.txt
Verified OK
$ od -t x1 hello.sig
0000000    30  45  02  20  55  5b  3c  3a  ab  2a  5f  70  de  62  a7  32
0000020    19  ea  e1  98  bb  13  1e  a7  00  9a  e4  52  ab  85  74  d8
0000040    c4  b0  4e  98  02  21  00  c0  aa  55  54  83  0f  54  33  f1
0000060    b4  53  fa  e9  f2  94  71  3c  5a  b7  83  a3  76  51  e1  24
0000100    84  d2  8c  41  dc  3d  5c
0000107
$ 

I suggest you not actually USE the public/private keypair provided above
given it is no longer secret.

      -- Mark