fix(provenance): fix multi-block armored keyring parsing on arbitrary alignments

Signed-off-by: Raphael Zanarelli <zanarelli.dev@gmail.com>

pkg/provenance/sign.go

@@ -394,12 +394,30 @@ func loadKeyRing(ringpath string) (openpgp.EntityList, error) {
 // way GnuPG imports them.
 func loadArmoredKeyRing(data []byte) (openpgp.EntityList, error) {
 	var ring openpgp.EntityList
-	r := bytes.NewReader(data)
-	for {
-		block, err := armor.Decode(r)
-		if errors.Is(err, io.EOF) {
+	for offset := 0; offset < len(data); {
+		start := bytes.Index(data[offset:], []byte("-----BEGIN "))
+		if start == -1 {
 			break
 		}
+		blockStart := offset + start
+
+		var blockBytes []byte
+		end := bytes.Index(data[blockStart:], []byte("-----END "))
+		if end == -1 {
+			blockBytes = data[blockStart:]
+			offset = len(data)
+		} else {
+			blockEnd := blockStart + end
+			if lineEnd := bytes.IndexByte(data[blockEnd:], '\n'); lineEnd == -1 {
+				blockBytes = data[blockStart:]
+				offset = len(data)
+			} else {
+				blockBytes = data[blockStart : blockEnd+lineEnd+1]
+				offset = blockEnd + lineEnd + 1
+			}
+		}
+
+		block, err := armor.Decode(bytes.NewReader(blockBytes))
 		if err != nil {
 			return nil, err
 		}

pkg/provenance/sign_test.go

@@ -19,6 +19,7 @@ import (
 	"bytes"
 	"crypto"
 	"errors"
+	"fmt"
 	"io"
 	"os"
 	"path/filepath"
@@ -199,6 +200,77 @@ func TestLoadKeyRingArmoredMultiBlock(t *testing.T) {
 	assert.Contains(t, names, testKeyName)
 }
 
+func rewrapArmoredKey(armored []byte, lineLen int) []byte {
+	lines := strings.Split(string(armored), "\n")
+	var out []string
+	var b64 strings.Builder
+	inBody := false
+
+	for _, line := range lines {
+		trimmed := strings.TrimRight(line, "\r")
+		if strings.HasPrefix(trimmed, "-----BEGIN ") {
+			out = append(out, trimmed)
+			inBody = false
+			continue
+		}
+		if strings.HasPrefix(trimmed, "-----END ") {
+			if b64.Len() > 0 {
+				raw := b64.String()
+				for i := 0; i < len(raw); i += lineLen {
+					end := i + lineLen
+					if end > len(raw) {
+						end = len(raw)
+					}
+					out = append(out, raw[i:end])
+				}
+				b64.Reset()
+			}
+			out = append(out, trimmed)
+			inBody = false
+			continue
+		}
+		if !inBody {
+			out = append(out, trimmed)
+			if trimmed == "" {
+				inBody = true
+			}
+			continue
+		}
+		if strings.HasPrefix(trimmed, "=") {
+			if b64.Len() > 0 {
+				raw := b64.String()
+				for i := 0; i < len(raw); i += lineLen {
+					end := i + lineLen
+					if end > len(raw) {
+						end = len(raw)
+					}
+					out = append(out, raw[i:end])
+				}
+				b64.Reset()
+			}
+			out = append(out, trimmed)
+			continue
+		}
+		b64.WriteString(trimmed)
+	}
+	return []byte(strings.Join(out, "\n") + "\n")
+}
+
+func TestLoadKeyRingArmoredMultiBlockLineAlignments(t *testing.T) {
+	raw, err := os.ReadFile(testMultiBlockArmored)
+	require.NoError(t, err)
+
+	for _, lineLen := range []int{32, 36, 40, 44, 48, 52, 56, 64} {
+		t.Run(fmt.Sprintf("lineLen_%d", lineLen), func(t *testing.T) {
+			rewrapped := rewrapArmoredKey(raw, lineLen)
+			k, err := loadArmoredKeyRing(rewrapped)
+			require.NoError(t, err)
+			require.Len(t, k, 2, "expected both keys to be loaded for line length %d", lineLen)
+		})
+	}
+}
+
+
 func TestLoadArmoredKeyRingRejectsNonKeyBlocks(t *testing.T) {
 	var buf bytes.Buffer
 	w, err := armor.Encode(&buf, "PGP MESSAGE", nil)