Ensure CN is included as a DNS SAN when FQDN.

CHANGELOG

@@ -1,5 +1,11 @@
 CHANGELOG
 
+v1.19.0 - 2026-02-12
+
+Added:
+- certlib/dump: DisplayCSR function for dumping Certificate Signing Request information.
+- certlib: MatchKeysCSR function for testing if a CSR's public key matches a private key.
+
 v1.18.0 - 2025-11-21
 
 Changed:

certlib/certgen/config.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"math/big"
 	"net"
+	"slices"
 	"strings"
 	"time"
 
@@ -88,12 +89,17 @@ func (cs CertificateRequest) Request(priv crypto.PrivateKey) (*x509.CertificateR
 		}
 	}
 
+	dnsNames := cs.Subject.DNSNames
+	if isFQDN(cs.Subject.CommonName) && !slices.Contains(dnsNames, cs.Subject.CommonName) {
+		dnsNames = append(dnsNames, cs.Subject.CommonName)
+	}
+
 	req := &x509.CertificateRequest{
 		PublicKeyAlgorithm: 0,
 		PublicKey:          getPublic(priv),
 		Subject:            subject,
 		EmailAddresses:     cs.Subject.Email,
-		DNSNames:           cs.Subject.DNSNames,
+		DNSNames:           dnsNames,
 		IPAddresses:        ipAddresses,
 	}
 
@@ -210,6 +216,32 @@ func (p Profile) SelfSign(req *x509.CertificateRequest, priv crypto.PrivateKey)
 	return p.SignRequest(certTemplate, req, priv)
 }
 
+// isFQDN returns true if s looks like a fully-qualified domain name.
+func isFQDN(s string) bool {
+	if s == "" {
+		return false
+	}
+	// Must contain at least one dot and no spaces.
+	if !strings.Contains(s, ".") || strings.ContainsAny(s, " \t") {
+		return false
+	}
+	// Each label must be non-empty and consist of letters, digits, or hyphens.
+	for label := range strings.SplitSeq(strings.TrimSuffix(s, "."), ".") {
+		if label == "" {
+			return false
+		}
+		for _, c := range label {
+			if !((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || c == '-') {
+				return false
+			}
+		}
+		if label[0] == '-' || label[len(label)-1] == '-' {
+			return false
+		}
+	}
+	return true
+}
+
 func SerialNumber() (*big.Int, error) {
 	serialNumberBytes := make([]byte, 20)
 	_, err := rand.Read(serialNumberBytes)

certlib/certgen/config_test.go

@@ -0,0 +1,104 @@
+package certgen
+
+import (
+	"slices"
+	"testing"
+)
+
+func TestIsFQDN(t *testing.T) {
+	tests := []struct {
+		input string
+		want  bool
+	}{
+		{"example.com", true},
+		{"sub.example.com", true},
+		{"example.com.", true}, // trailing dot
+		{"localhost", false},   // no dot
+		{"", false},
+		{"foo bar.com", false}, // space
+		{"-bad.com", false},    // leading hyphen
+		{"bad-.com", false},    // trailing hyphen
+		{"a..b.com", false},    // empty label
+	}
+
+	for _, tt := range tests {
+		got := isFQDN(tt.input)
+		if got != tt.want {
+			t.Errorf("isFQDN(%q) = %v, want %v", tt.input, got, tt.want)
+		}
+	}
+}
+
+func TestRequestAddsFQDNAsDNSSAN(t *testing.T) {
+	creq := &CertificateRequest{
+		KeySpec: KeySpec{Algorithm: "ecdsa", Size: 256},
+		Subject: Subject{
+			CommonName:   "example.com",
+			Organization: "Test Org",
+		},
+		Profile: Profile{
+			Expiry: "1h",
+		},
+	}
+
+	_, req, err := creq.Generate()
+	if err != nil {
+		t.Fatalf("Generate() error: %v", err)
+	}
+
+	if !slices.Contains(req.DNSNames, "example.com") {
+		t.Errorf("expected DNS SAN to contain %q, got %v", "example.com", req.DNSNames)
+	}
+}
+
+func TestRequestFQDNNotDuplicated(t *testing.T) {
+	creq := &CertificateRequest{
+		KeySpec: KeySpec{Algorithm: "ecdsa", Size: 256},
+		Subject: Subject{
+			CommonName:   "example.com",
+			Organization: "Test Org",
+			DNSNames:     []string{"example.com", "www.example.com"},
+		},
+		Profile: Profile{
+			Expiry: "1h",
+		},
+	}
+
+	_, req, err := creq.Generate()
+	if err != nil {
+		t.Fatalf("Generate() error: %v", err)
+	}
+
+	count := 0
+	for _, name := range req.DNSNames {
+		if name == "example.com" {
+			count++
+		}
+	}
+
+	if count != 1 {
+		t.Errorf("expected exactly 1 occurrence of %q in DNS SANs, got %d: %v", "example.com", count, req.DNSNames)
+	}
+}
+
+func TestRequestNonFQDNCommonNameNotAdded(t *testing.T) {
+	creq := &CertificateRequest{
+		KeySpec: KeySpec{Algorithm: "ecdsa", Size: 256},
+		Subject: Subject{
+			CommonName:   "localhost",
+			Organization: "Test Org",
+		},
+		Profile: Profile{
+			Expiry: "1h",
+		},
+	}
+
+	_, req, err := creq.Generate()
+	if err != nil {
+		t.Fatalf("Generate() error: %v", err)
+	}
+
+	if slices.Contains(req.DNSNames, "localhost") {
+		t.Errorf("expected DNS SANs to not contain %q, got %v", "localhost", req.DNSNames)
+	}
+}

certlib/dump/dump.go

@@ -165,6 +165,28 @@ func certPublic(cert *x509.Certificate) string {
 	}
 }
 
+func csrPublic(csr *x509.CertificateRequest) string {
+	switch pub := csr.PublicKey.(type) {
+	case *rsa.PublicKey:
+		return fmt.Sprintf("RSA-%d", pub.N.BitLen())
+	case *ecdsa.PublicKey:
+		switch pub.Curve {
+		case elliptic.P256():
+			return "ECDSA-prime256v1"
+		case elliptic.P384():
+			return "ECDSA-secp384r1"
+		case elliptic.P521():
+			return "ECDSA-secp521r1"
+		default:
+			return "ECDSA (unknown curve)"
+		}
+	case *dsa.PublicKey:
+		return "DSA"
+	default:
+		return "Unknown"
+	}
+}
+
 func DisplayName(name pkix.Name) string {
 	var ns []string
 
@@ -333,3 +355,36 @@ func DisplayCert(w io.Writer, cert *x509.Certificate, showHash bool) {
 		}
 	}
 }
+
+func DisplayCSR(w io.Writer, csr *x509.CertificateRequest, showHash bool) {
+	fmt.Fprintln(w, "CERTIFICATE REQUEST")
+	if showHash {
+		fmt.Fprintln(w, wrap(fmt.Sprintf("SHA256: %x", sha256.Sum256(csr.Raw)), 0))
+	}
+
+	fmt.Fprintln(w, wrap("Subject: "+DisplayName(csr.Subject), 0))
+	fmt.Fprintf(w, "\tSignature algorithm: %s / %s\n", sigAlgoPK(csr.SignatureAlgorithm),
+		sigAlgoHash(csr.SignatureAlgorithm))
+	fmt.Fprintln(w, "Details:")
+	wrapPrint("Public key: "+csrPublic(csr), 1)
+
+	validNames := make([]string, 0, len(csr.DNSNames)+len(csr.EmailAddresses)+len(csr.IPAddresses)+len(csr.URIs))
+	for i := range csr.DNSNames {
+		validNames = append(validNames, "dns:"+csr.DNSNames[i])
+	}
+
+	for i := range csr.EmailAddresses {
+		validNames = append(validNames, "email:"+csr.EmailAddresses[i])
+	}
+
+	for i := range csr.IPAddresses {
+		validNames = append(validNames, "ip:"+csr.IPAddresses[i].String())
+	}
+
+	for i := range csr.URIs {
+		validNames = append(validNames, "uri:"+csr.URIs[i].String())
+	}
+
+	sans := fmt.Sprintf("SANs (%d): %s\n", len(validNames), strings.Join(validNames, ", "))
+	wrapPrint(sans, 1)
+}

certlib/keymatch.go

@@ -133,3 +133,48 @@ func MatchKeys(cert *x509.Certificate, priv crypto.Signer) (bool, string) {
 		return false, fmt.Sprintf("unrecognised private key type: %T", priv.Public())
 	}
 }
+
+// MatchKeysCSR determines whether the CSR's public key matches the given private key.
+// It returns true if they match; otherwise, it returns false and a human-friendly reason.
+func MatchKeysCSR(csr *x509.CertificateRequest, priv crypto.Signer) (bool, string) {
+	switch keyPub := priv.Public().(type) {
+	case *rsa.PublicKey:
+		switch csrPub := csr.PublicKey.(type) {
+		case *rsa.PublicKey:
+			if matchRSA(csrPub, keyPub) {
+				return true, ""
+			}
+			return false, "public keys don't match"
+		case *ecdsa.PublicKey:
+			return false, "RSA private key, EC public key"
+		default:
+			return false, fmt.Sprintf("unsupported CSR public key type: %T", csr.PublicKey)
+		}
+	case *ecdsa.PublicKey:
+		switch csrPub := csr.PublicKey.(type) {
+		case *ecdsa.PublicKey:
+			if matchECDSA(csrPub, keyPub) {
+				return true, ""
+			}
+			// Determine a more precise reason
+			kc := getECCurve(keyPub)
+			cc := getECCurve(csrPub)
+			if kc == curveInvalid {
+				return false, "invalid private key curve"
+			}
+			if cc == curveRSA {
+				return false, "private key is EC, CSR is RSA"
+			}
+			if kc != cc {
+				return false, "EC curves don't match"
+			}
+			return false, "public keys don't match"
+		case *rsa.PublicKey:
+			return false, "private key is EC, CSR is RSA"
+		default:
+			return false, fmt.Sprintf("unsupported CSR public key type: %T", csr.PublicKey)
+		}
+	default:
+		return false, fmt.Sprintf("unrecognised private key type: %T", priv.Public())
+	}
+}

cmd/ccfind/main.go

@@ -0,0 +1,46 @@
+package main
+
+// Prompt:
+// The current main.go should accept a list of paths to search. In each
+// of those paths, without recursing, it should find all files ending in
+// C/C++ source extensions and print them one per line.
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"slices"
+	"strings"
+)
+
+var extensions = []string{
+	".c", ".cpp", ".cc", ".cxx",
+	".h", ".hpp", ".hh", ".hxx",
+}
+
+func main() {
+	if len(os.Args) < 2 {
+		fmt.Fprintf(os.Stderr, "Usage: %s <path> [path...]\n", os.Args[0])
+		os.Exit(1)
+	}
+
+	for _, path := range os.Args[1:] {
+		entries, err := os.ReadDir(path)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Error reading %s: %v\n", path, err)
+			continue
+		}
+
+		for _, entry := range entries {
+			if entry.IsDir() {
+				continue
+			}
+
+			name := entry.Name()
+			ext := filepath.Ext(name)
+			if slices.Contains(extensions, strings.ToLower(ext)) {
+				fmt.Println(filepath.Join(path, name))
+			}
+		}
+	}
+}