func()

in ietf-cms/protocol/protocol.go [628:738]
88 lines of code
20 McCabe index (conditional complexity)

func (sd *SignedData) AddSignerInfo(chain []*x509.Certificate, signer crypto.Signer) error {
	// figure out which certificate is associated with signer.
	pub, err := x509.MarshalPKIXPublicKey(signer.Public())
	if err != nil {
		return err
	}

	var (
		cert    *x509.Certificate
		certPub []byte
	)

	for _, c := range chain {
		if err = sd.AddCertificate(c); err != nil {
			return err
		}

		if certPub, err = x509.MarshalPKIXPublicKey(c.PublicKey); err != nil {
			return err
		}

		if bytes.Equal(pub, certPub) {
			cert = c
		}
	}
	if cert == nil {
		return ErrNoCertificate
	}

	sid, err := NewIssuerAndSerialNumber(cert)
	if err != nil {
		return err
	}

	digestAlgorithmID := digestAlgorithmForPublicKey(pub)

	signatureAlgorithmOID, ok := oid.X509PublicKeyAndDigestAlgorithmToSignatureAlgorithm[cert.PublicKeyAlgorithm][digestAlgorithmID.Algorithm.String()]
	if !ok {
		return errors.New("unsupported certificate public key algorithm")
	}

	signatureAlgorithmID := pkix.AlgorithmIdentifier{Algorithm: signatureAlgorithmOID}

	si := SignerInfo{
		Version:            1,
		SID:                sid,
		DigestAlgorithm:    digestAlgorithmID,
		SignedAttrs:        nil,
		SignatureAlgorithm: signatureAlgorithmID,
		Signature:          nil,
		UnsignedAttrs:      nil,
	}

	// Get the message
	content, err := sd.EncapContentInfo.EContentValue()
	if err != nil {
		return err
	}
	if content == nil {
		return errors.New("already detached")
	}

	// Digest the message.
	hash, err := si.Hash()
	if err != nil {
		return err
	}
	md := hash.New()
	if _, err = md.Write(content); err != nil {
		return err
	}

	// Build our SignedAttributes
	stAttr, err := NewAttribute(oid.AttributeSigningTime, time.Now().UTC())
	if err != nil {
		return err
	}
	mdAttr, err := NewAttribute(oid.AttributeMessageDigest, md.Sum(nil))
	if err != nil {
		return err
	}
	ctAttr, err := NewAttribute(oid.AttributeContentType, sd.EncapContentInfo.EContentType)
	if err != nil {
		return err
	}

	// sort attributes to match required order in marshaled form
	si.SignedAttrs, err = sortAttributes(stAttr, mdAttr, ctAttr)
	if err != nil {
		return err
	}

	// Signature is over the marshaled signed attributes
	sm, err := si.SignedAttrs.MarshaledForSigning()
	if err != nil {
		return err
	}
	smd := hash.New()
	if _, errr := smd.Write(sm); errr != nil {
		return errr
	}
	if si.Signature, err = signer.Sign(rand.Reader, smd.Sum(nil), hash); err != nil {
		return err
	}

	sd.addDigestAlgorithm(si.DigestAlgorithm)

	sd.SignerInfos = append(sd.SignerInfos, si)

	return nil
}