OpenSSL

ECDSA

# Create private key 
openssl ecparam -name secp256k1 -genkey -noout -out private-key.pem

# Extract public key from private key
openssl ec -in private-key.pem -pubout -out public-key.pem

# Generate signature
openssl dgst -sha256 -sign private-key.pem -out signature.bin message.txt

# Verify signature
openssl dgst -sha256 -verify public-key.pem -signature signature.bin message.txt

RSA

# Create private key 
openssl genrsa -aes256 -out private.pem 2048

# Extract public key from private key
openssl rsa -in private.pem -outform PEM -pubout -out public.pem

# Generate signature
openssl dgst -sha256 -sign private.pem -out signature.bin message.txt

# Verify signature
openssl dgst -sha256 -verify public.pem -signature signature.bin message.txt