EC Key in PEM File Format

EC Cryptography Tutorials - Herong's Tutorial Examples

∟EC Key in PEM File Format

This section provides a tutorial example on the EC key PEM file format. EC domain parameters are stored together with the private key.

When EC private and public keys are stored in a file, what file format is used?

Let's open the EC key file generated by the OpenSSL tool and see:

herong> openssl ecparam -genkey -name secp256k1 \
   -out ec_key.pem -param_enc explicit

herong> type ec_key.pem

-----BEGIN EC PARAMETERS-----
MIGiAgEBMCwGByqGSM49AQECIQD////////////////////////////////////+
///8LzAGBAEABAEHBEEEeb5mfvncu6xVoGKVzocLBwKb/NstzijZWfKBWxb4F5hI
Otp3JqPEZV2k+/wOEQio/Re0SKaFVBmcR9CP+xDUuAIhAP//////////////////
//66rtzmr0igO7/SXozQNkFBAgEB
-----END EC PARAMETERS-----
-----BEGIN EC PRIVATE KEY-----
MIIBEwIBAQQg8upej8Y28VkB8iO+ak93N0rBtyt/YBxNZJmg4UV0MbqggaUwgaIC
AQEwLAYHKoZIzj0BAQIhAP////////////////////////////////////7///wv
MAYEAQAEAQcEQQR5vmZ++dy7rFWgYpXOhwsHApv82y3OKNlZ8oFbFvgXmEg62ncm
o8RlXaT7/A4RCKj9F7RIpoVUGZxH0I/7ENS4AiEA/////////////////////rqu
3OavSKA7v9JejNA2QUECAQGhRANCAAT7e7C7o/lXxfS1yxNO9i23Sz1VC3Z3jnvq
C1tW1TQNNYEHeb2+D06ZDVZtC/gCDtPQ/Zu5VENHIasAmtbDHeRq
-----END EC PRIVATE KEY-----

It seems that the EC private key is stored separately from the domain parameters.

If we keep the private key part only in a file, is it still a valid private key file? Let's copy the private key part to a new file, ec_key_only.pem, and try it:

herong> type ec_key_only.pem
-----BEGIN EC PRIVATE KEY-----
MIIBEwIBAQQg8upej8Y28VkB8iO+ak93N0rBtyt/YBxNZJmg4UV0MbqggaUwgaIC
AQEwLAYHKoZIzj0BAQIhAP////////////////////////////////////7///wv
MAYEAQAEAQcEQQR5vmZ++dy7rFWgYpXOhwsHApv82y3OKNlZ8oFbFvgXmEg62ncm
o8RlXaT7/A4RCKj9F7RIpoVUGZxH0I/7ENS4AiEA/////////////////////rqu
3OavSKA7v9JejNA2QUECAQGhRANCAAT7e7C7o/lXxfS1yxNO9i23Sz1VC3Z3jnvq
C1tW1TQNNYEHeb2+D06ZDVZtC/gCDtPQ/Zu5VENHIasAmtbDHeRq
-----END EC PRIVATE KEY-----

herong> openssl ec -in ec_key_only.pem -noout -text
read EC key
Private-Key: (256 bit)
priv:
    00:f2:ea:5e:8f:c6:36:f1:59:01:f2:23:be:6a:4f:
    77:37:4a:c1:b7:2b:7f:60:1c:4d:64:99:a0:e1:45:
    74:31:ba
pub:
    04:fb:7b:b0:bb:a3:f9:57:c5:f4:b5:cb:13:4e:f6:
    2d:b7:4b:3d:55:0b:76:77:8e:7b:ea:0b:5b:56:d5:
    34:0d:35:81:07:79:bd:be:0f:4e:99:0d:56:6d:0b:
    f8:02:0e:d3:d0:fd:9b:b9:54:43:47:21:ab:00:9a:
    d6:c3:1d:e4:6a
Field Type: prime-field
Prime:
    00:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:
    ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:fe:ff:
    ff:fc:2f
A:    0
B:    7 (0x7)
Generator (uncompressed):
    04:79:be:66:7e:f9:dc:bb:ac:55:a0:62:95:ce:87:
    0b:07:02:9b:fc:db:2d:ce:28:d9:59:f2:81:5b:16:
    f8:17:98:48:3a:da:77:26:a3:c4:65:5d:a4:fb:fc:
    0e:11:08:a8:fd:17:b4:48:a6:85:54:19:9c:47:d0:
    8f:fb:10:d4:b8
Order:
    00:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:ff:
    ff:fe:ba:ae:dc:e6:af:48:a0:3b:bf:d2:5e:8c:d0:
    36:41:41
Cofactor:  1 (0x1)