1 files changed, 92 insertions, 0 deletions
diff --git a/internal/identity/verify.go b/internal/identity/verify.go
new file mode 100644
index 0000000..e337e07
--- /dev/null
+++ b/internal/identity/verify.go
@@ -0,0 +1,92 @@
+package identity
+
+import (
+	"crypto/ed25519"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"io"
+	"net/mail"
+	"strings"
+
+	"aegis/internal/cryptokit"
+)
+
+type VerificationResult struct {
+	VFaceValid        bool
+	IdentityHashValid bool
+	FaceValid         bool
+	SignaturePresent  bool
+	SignatureValid    bool
+	PublicKey         string
+	IdentityHash      string
+	PNGHash           string
+	Error             error
+}
+
+func VerifyArticle(article string) VerificationResult {
+	message, err := mail.ReadMessage(strings.NewReader(article))
+	if err != nil {
+		return VerificationResult{Error: fmt.Errorf("parse article: %w", err)}
+	}
+	from, err := mail.ParseAddress(message.Header.Get("From"))
+	if err != nil {
+		return VerificationResult{Error: fmt.Errorf("parse From: %w", err)}
+	}
+	publicKey := strings.TrimSpace(message.Header.Get("X-Ed25519-Pub"))
+	result := VerificationResult{PublicKey: publicKey, IdentityHash: strings.TrimSpace(message.Header.Get("Identity-Hash")), PNGHash: strings.TrimSpace(message.Header.Get("X-VFace-PNG-SHA256"))}
+	profile, profileErr := GenerateVFace(from.Name, from.Address, publicKey)
+	if profileErr != nil {
+		result.Error = profileErr
+		return result
+	}
+	result.IdentityHashValid = strings.EqualFold(strings.TrimPrefix(result.IdentityHash, "sha256:"), profile.IdentityHash)
+	result.FaceValid = strings.TrimSpace(message.Header.Get("Face")) == profile.FaceBase64
+	result.VFaceValid = result.IdentityHashValid && result.FaceValid
+	if result.PNGHash != "" && !strings.EqualFold(strings.TrimPrefix(result.PNGHash, "sha256:"), profile.PNGHash) {
+		result.VFaceValid = false
+	}
+	signature := strings.TrimSpace(message.Header.Get("X-Ed25519-Sig"))
+	if signature == "" {
+		value := strings.TrimSpace(message.Header.Get("X-Aegis-Signature"))
+		if parts := strings.SplitN(value, ";", 2); len(parts) == 2 && strings.EqualFold(strings.TrimSpace(parts[0]), "ed25519") {
+			signature = strings.TrimSpace(parts[1])
+		}
+	}
+	if signature == "" {
+		return result
+	}
+	result.SignaturePresent = true
+	signatureBytes, decodeErr := base64.StdEncoding.DecodeString(signature)
+	if decodeErr != nil || len(signatureBytes) != ed25519.SignatureSize {
+		result.Error = errors.New("invalid Ed25519 signature encoding")
+		return result
+	}
+	body, readErr := io.ReadAll(io.LimitReader(message.Body, 16<<20))
+	if readErr != nil {
+		result.Error = fmt.Errorf("read article body: %w", readErr)
+		return result
+	}
+	key, keyErr := decodePublicKey(publicKey)
+	if keyErr != nil {
+		result.Error = keyErr
+		return result
+	}
+	result.SignatureValid = ed25519.Verify(key, body, signatureBytes)
+	if !result.SignatureValid {
+		result.Error = errors.New("Ed25519 signature verification failed")
+	}
+	return result
+}
+
+func decodePublicKey(value string) (ed25519.PublicKey, error) {
+	canonicalText, err := cryptokit.CanonicalEd25519PublicKey(value)
+	if err != nil {
+		return nil, err
+	}
+	canonical, err := base64.StdEncoding.DecodeString(canonicalText)
+	if err != nil {
+		return nil, fmt.Errorf("decode Ed25519 public key: %w", err)
+	}
+	return ed25519.PublicKey(canonical), nil
+}