ECDSA usage from Ruby.

ecdsa_example.rb

require 'openssl'
require 'base64'

# ===== \/ sign =====
# generate keys
key = OpenSSL::PKey::EC.new("secp256k1")
key.generate_key
public_key = key.public_key
public_key_hex = public_key.to_bn.to_s(16).downcase # public key in hex format

# sign a message
data = "My message to sign"
signature = key.dsa_sign_asn1(data)
signature_base64 = Base64.encode64(signature).gsub("\n", "")

# ===== \/ verify =====
# rebuild key
group = OpenSSL::PKey::EC::Group.new('secp256k1')
key = OpenSSL::PKey::EC.new(group)
# create point from hex key
public_key_bn = OpenSSL::BN.new(public_key_hex, 16)
public_key = OpenSSL::PKey::EC::Point.new(group, public_key_bn)
key.public_key = public_key

# verify message
data = "My message to sign"
signature = Base64.decode64(signature_base64)
key.dsa_verify_asn1(data, signature)

If you are getting an error about immutability, use the following

key = OpenSSL::PKey::EC.generate("secp256k1")

instead of

key = OpenSSL::PKey::EC.new("secp256k1") # IT'S WRONG FOR OPENSSL 3