1package dns
2
3import (
4	"crypto/sha256"
5	"crypto/x509"
6	"encoding/hex"
7)
8
9// Sign creates a SMIMEA record from an SSL certificate.
10func (r *SMIMEA) Sign(usage, selector, matchingType int, cert *x509.Certificate) (err error) {
11	r.Hdr.Rrtype = TypeSMIMEA
12	r.Usage = uint8(usage)
13	r.Selector = uint8(selector)
14	r.MatchingType = uint8(matchingType)
15
16	r.Certificate, err = CertificateToDANE(r.Selector, r.MatchingType, cert)
17	if err != nil {
18		return err
19	}
20	return nil
21}
22
23// Verify verifies a SMIMEA record against an SSL certificate. If it is OK
24// a nil error is returned.
25func (r *SMIMEA) Verify(cert *x509.Certificate) error {
26	c, err := CertificateToDANE(r.Selector, r.MatchingType, cert)
27	if err != nil {
28		return err // Not also ErrSig?
29	}
30	if r.Certificate == c {
31		return nil
32	}
33	return ErrSig // ErrSig, really?
34}
35
36// SMIMEAName returns the ownername of a SMIMEA resource record as per the
37// format specified in RFC 'draft-ietf-dane-smime-12' Section 2 and 3
38func SMIMEAName(email, domain string) (string, error) {
39	hasher := sha256.New()
40	hasher.Write([]byte(email))
41
42	// RFC Section 3: "The local-part is hashed using the SHA2-256
43	// algorithm with the hash truncated to 28 octets and
44	// represented in its hexadecimal representation to become the
45	// left-most label in the prepared domain name"
46	return hex.EncodeToString(hasher.Sum(nil)[:28]) + "." + "_smimecert." + domain, nil
47}
48