code: func Check(d *certdata.Data) *errors.Errors {
  	var e = errors.New(nil)
  
  	// Check if we use SHA1 or less (MD5, MD2)
  	if d.Cert.SignatureAlgorithm > x509.SHA1WithRSA &&
  		d.Cert.SignatureAlgorithm != x509.DSAWithSHA1 &&
  		d.Cert.SignatureAlgorithm != x509.ECDSAWithSHA1 {
  		return e
  	}
  
  	if d.Cert.NotBefore.After(time.Date(2016, 1, 1, 0, 0, 0, 0, time.UTC)) {
  		e.Err("Certificate is using SHA1, but is issued on/after 1 Jan 2016")
  		return e
  	}
  
  	if d.Cert.NotBefore.After(time.Date(2015, 1, 16, 0, 0, 0, 0, time.UTC)) &&
  		d.Cert.NotAfter.After(time.Date(2017, 1, 1, 0, 0, 0, 0, time.UTC)) {
  		e.Err("Certificate is using SHA1, but is still valid on/after 1 Jan 2017")
  		return e
  	}
  
  	return nil
  }
docs: // Check performs a strict verification on the extension according to the standard(s)