Drop an X.509 certificate to extract its public key as a Base64 SPKI string. Subject, issuer, validity dates, key algorithm, and serial number are also parsed and displayed. Nothing leaves your browser.
BEGIN CERTIFICATE (X.509 PEM), binary DER .cer / .der, and BEGIN PUBLIC KEY (SPKI).openssl pkcs12 -in file.p12 -nokeys -clcerts | openssl x509 -out cert.pem