2.1. Manage EC Keys

calendar Sep 22, 2024 · 3 min read · pki tls ssl ec ed25519 ecdsa eddsa openssl  ·
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This chapter introduces how to generate, convert, encode, encrypt, decrypt EC keys using OpenSSL command-line tools.

Generate EC Keys

According to the key length, there are three types of keys:

1# NIST P-256
2openssl ecparam -genkey -name prime256v1 -noout -out es256-raw.pem
3# NIST P-384
4openssl ecparam -genkey -name secp384r1 -noout -out es384-raw.pem
5# NIST P-521
6openssl ecparam -genkey -name secp521r1 -noout -out es521-raw.pem

However, if you choose to use curve25519, you must use the genpkey subcommand, and the key must be in PKCS#8 format.

1openssl genpkey -algorithm ed25519 -out ed25519-raw.pem # The generated key file is in PKCS#8 format
2
3openssl genpkey -algorithm x25519 -out x25519-raw.pem # The generated key file is in PKCS#8 format

Note:

  • The key is generated without encryption protection.
  • If you want to use curve25519 in a certificate, please use ed25519 instead of x25519, because the public key in X.509 certificates is used for signing, not for key exchange.

Encryption and Decryption of Keys

Encrypt Keys

 1# PKCS#1
 2openssl ec -aes-256-cfb -in es384-raw.pem -out es384.pem
 3
 4# PKCS#8
 5openssl pkcs8 \
 6    -topk8 \
 7    -inform PEM \
 8    -v2 aes256 \
 9    -in ed25519-p8-raw.pem \
10    -out ed25519-p8.pem

Decrypt Keys

1openssl ec -in es384-raw.pem -out es384.pem
2
3# PKCS#8
4openssl pkcs8 \
5    -inform PEM \
6    -in ed25519-p8.pem \
7    -out ed25519-p8-raw.pem

Extract Public Key

1# This command accepts both PKCS#1 and PKCS#8 encoded private keys
2openssl ec -in es384.pem -pubout -out es384.pub
3openssl ec -in ed25519.pem -pubout -out ed25519.pub

View Private Key Information

1# This command accepts both PKCS#1 and PKCS#8 encoded private keys
2openssl ec -text -noout -in es384-raw.pem

View Public Key Information

1openssl ec -pubin -text -noout -in es384.pub
2openssl ec -pubin -text -noout -in ed25519.pub

Convert Keys

The conversion between EC keys and PKCS#8 is similar to RSA.

openssl ec command accepts -inform and -outform too, so the DER/PEM conversion of EC keys is the same as RSA keys.

Test Keys

 1openssl rand -out tmp.dat 4096
 2
 3# Sign the random file with the private key using ECDSA-SHA-256
 4
 5openssl dgst -sha256 -sign es384-raw.pem -out tmp.dat.sig tmp.dat
 6openssl dgst -sha256 -verify es384.pub -signature tmp.dat.sig tmp.dat
 7
 8# Test ECDH (curve25519)
 9
10openssl genpkey -algorithm x25519 -out x25519-a.pem
11openssl ec -in x25519-a.pem -pubout -out x25519-a.pub
12
13openssl genpkey -algorithm x25519 -out x25519-b.pem
14openssl ec -in x25519-b.pem -pubout -out x25519-b.pub
15
16openssl pkeyutl -derive -inkey x25519-a.pem -peerkey x25519-b.pub -out x25519-axb.bin
17openssl pkeyutl -derive -inkey x25519-b.pem -peerkey x25519-a.pub -out x25519-bxa.bin
18
19base64 x25519-axb.bin
20base64 x25519-bxa.bin
21
22rm x25519-*.*
23
24# Test EdDSA (Ed25519) Signing
25
26openssl genpkey -algorithm ed25519 -out ed25519.pem
27openssl ec -in ed25519.pem -pubout -out ed25519.pub
28
29openssl pkeyutl -sign -inkey ed25519.pem -rawin -in tmp.dat -out tmp.dat.sig
30openssl pkeyutl -verify -pubin -inkey ed25519.pub -sigfile tmp.dat.sig -rawin -in tmp.dat
31
32rm ed25519.*
33
34rm tmp.*

Ok, all above are the common operations of EC keys.

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