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Merged
pgundlach merged 1 commit into from
Jun 23, 2026
Merged

Cover encryption param parsing (crypt) #17

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130 changes: 113 additions & 17 deletions crypt_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -129,18 +129,10 @@ func rc4Crypt(key, data []byte) []byte {
return out
}

// buildRC4EncryptedStreamPDF builds a V2/R3 RC4-encrypted PDF (empty password)
// whose object 4 is a stream carrying RC4-encrypted plaintext.
func buildRC4EncryptedStreamPDF(t *testing.T, plaintext []byte) []byte {
t.Helper()
owner := bytes.Repeat([]byte{0x5a}, 32)
id0 := bytes.Repeat([]byte{0x7c}, 16)
const bits = 128
var p int32 = -44
fileKey := emptyPwRC4Key(owner, id0, p, bits)
u := emptyPwU(fileKey, id0)
enc := rc4Crypt(objKeyRC4(fileKey, 4, 0), plaintext)

// assembleEncryptedPDF builds a classical-xref PDF — catalog (1), pages (2),
// the given /Encrypt dict body (3), and an already-encrypted stream (4) — with
// the trailer wired to /Encrypt 3 0 R and /ID [id0 id0].
func assembleEncryptedPDF(encryptBody string, encStream, id0 []byte) []byte {
var buf bytes.Buffer
off := func() int { return buf.Len() }
fmt.Fprint(&buf, "%PDF-1.7\n%\xE2\xE3\xCF\xD3\n")
Expand All @@ -150,12 +142,10 @@ func buildRC4EncryptedStreamPDF(t *testing.T, plaintext []byte) []byte {
offsets[2] = off()
fmt.Fprint(&buf, "2 0 obj\n<< /Type /Pages /Count 0 /Kids [] >>\nendobj\n")
offsets[3] = off()
fmt.Fprintf(&buf,
"3 0 obj\n<< /Filter /Standard /V 2 /R 3 /Length %d /O <%s> /U <%s> /P %d >>\nendobj\n",
bits, hex.EncodeToString(owner), hex.EncodeToString(u), p)
fmt.Fprintf(&buf, "3 0 obj\n%s\nendobj\n", encryptBody)
offsets[4] = off()
fmt.Fprintf(&buf, "4 0 obj\n<< /Length %d >>\nstream\n", len(enc))
buf.Write(enc)
fmt.Fprintf(&buf, "4 0 obj\n<< /Length %d >>\nstream\n", len(encStream))
buf.Write(encStream)
fmt.Fprint(&buf, "\nendstream\nendobj\n")

xrefOff := off()
Expand All @@ -171,6 +161,40 @@ func buildRC4EncryptedStreamPDF(t *testing.T, plaintext []byte) []byte {
return buf.Bytes()
}

// buildRC4EncryptedStreamPDF builds a V2/R3 RC4-encrypted PDF (empty password)
// whose object 4 is a stream carrying RC4-encrypted plaintext.
func buildRC4EncryptedStreamPDF(t *testing.T, plaintext []byte) []byte {
t.Helper()
owner := bytes.Repeat([]byte{0x5a}, 32)
id0 := bytes.Repeat([]byte{0x7c}, 16)
const bits = 128
var p int32 = -44
fileKey := emptyPwRC4Key(owner, id0, p, bits)
u := emptyPwU(fileKey, id0)
enc := rc4Crypt(objKeyRC4(fileKey, 4, 0), plaintext)
body := fmt.Sprintf("<< /Filter /Standard /V 2 /R 3 /Length %d /O <%s> /U <%s> /P %d >>",
bits, hex.EncodeToString(owner), hex.EncodeToString(u), p)
return assembleEncryptedPDF(body, enc, id0)
}

// buildV4RC4EncryptedStreamPDF builds a V4/R4 PDF whose StdCF crypt filter uses
// CFM /V2 (RC4) — same empty-password key derivation as V2/R3, reached through
// the V4 /CF + /StmF parsing path.
func buildV4RC4EncryptedStreamPDF(t *testing.T, plaintext []byte) []byte {
t.Helper()
owner := bytes.Repeat([]byte{0x5a}, 32)
id0 := bytes.Repeat([]byte{0x7c}, 16)
const bits = 128
var p int32 = -44
fileKey := emptyPwRC4Key(owner, id0, p, bits)
u := emptyPwU(fileKey, id0)
enc := rc4Crypt(objKeyRC4(fileKey, 4, 0), plaintext)
body := fmt.Sprintf("<< /Filter /Standard /V 4 /R 4 /Length %d /O <%s> /U <%s> /P %d "+
"/CF << /StdCF << /CFM /V2 /Length 16 >> >> /StmF /StdCF /StrF /StdCF /EncryptMetadata true >>",
bits, hex.EncodeToString(owner), hex.EncodeToString(u), p)
return assembleEncryptedPDF(body, enc, id0)
}

// Open must accept an RC4-encrypted PDF secured with the empty user password
// and decrypt its stream content end-to-end.
func TestOpenDecryptsRC4Stream(t *testing.T) {
Expand All @@ -189,3 +213,75 @@ func TestOpenDecryptsRC4Stream(t *testing.T) {
t.Fatalf("decrypted stream mismatch:\n got %q\nwant %q", got, plaintext)
}
}

// The V4 path resolves the stream cipher through /CF + /StmF rather than /V
// directly, so it must be exercised end-to-end too.
func TestOpenDecryptsV4RC4Stream(t *testing.T) {
plaintext := []byte("BT (V4 crypt filter) Tj ET")
data := buildV4RC4EncryptedStreamPDF(t, plaintext)
r, err := Open(bytes.NewReader(data))
if err != nil {
t.Fatalf("Open: %v", err)
}
defer r.Close()
got, err := r.DecodeStream(Reference{Number: 4, Generation: 0})
if err != nil {
t.Fatalf("DecodeStream: %v", err)
}
if !bytes.Equal(got, plaintext) {
t.Fatalf("V4 decrypted stream mismatch:\n got %q\nwant %q", got, plaintext)
}
}

// buildPDFWithEncryptObj wraps an arbitrary /Encrypt dict body as object 3 of a
// classical-xref PDF, with the trailer pointing /Encrypt at it.
func buildPDFWithEncryptObj(t *testing.T, encryptBody string) []byte {
t.Helper()
var buf bytes.Buffer
off := func() int { return buf.Len() }
fmt.Fprint(&buf, "%PDF-1.7\n%\xE2\xE3\xCF\xD3\n")
offsets := make([]int, 4)
offsets[1] = off()
fmt.Fprint(&buf, "1 0 obj\n<< /Type /Catalog /Pages 2 0 R >>\nendobj\n")
offsets[2] = off()
fmt.Fprint(&buf, "2 0 obj\n<< /Type /Pages /Count 0 /Kids [] >>\nendobj\n")
offsets[3] = off()
fmt.Fprintf(&buf, "3 0 obj\n%s\nendobj\n", encryptBody)
xrefOff := off()
fmt.Fprint(&buf, "xref\n0 4\n")
fmt.Fprintf(&buf, "%010d %05d f \n", 0, 65535)
for i := 1; i <= 3; i++ {
fmt.Fprintf(&buf, "%010d %05d n \n", offsets[i], 0)
}
id := "<00112233445566778899aabbccddeeff>"
fmt.Fprintf(&buf, "trailer\n<< /Size 4 /Root 1 0 R /Encrypt 3 0 R /ID [%s %s] >>\n", id, id)
fmt.Fprintf(&buf, "startxref\n%d\n%%%%EOF\n", xrefOff)
return buf.Bytes()
}

// Only the /Standard security handler is supported; any other /Filter must be
// rejected rather than silently treated as unencrypted.
func TestEncryptNonStandardFilterRejected(t *testing.T) {
data := buildPDFWithEncryptObj(t, "<< /Filter /FooSecurity /V 2 /R 3 /Length 128 >>")
if _, err := Open(bytes.NewReader(data)); err == nil {
t.Fatal("expected an error for a non-Standard /Filter, got nil")
}
}

// Malformed /Encrypt dictionaries (wrong type, missing fields, short V5 entries)
// must surface as errors during Open, never panics.
func TestEncryptMalformedNoPanic(t *testing.T) {
cases := map[string]string{
"encrypt not a dict": "42",
"missing V and R": "<< /Filter /Standard >>",
"short O and U": "<< /Filter /Standard /V 2 /R 3 /Length 128 /O <00> /U <00> /P 0 >>",
"v5 short entries": "<< /Filter /Standard /V 5 /R 6 /Length 256 /O <00> /U <00> /OE <00> /UE <00> /Perms <00> /P 0 >>",
}
for name, body := range cases {
t.Run(name, func(t *testing.T) {
if _, err := Open(bytes.NewReader(buildPDFWithEncryptObj(t, body))); err == nil {
t.Fatal("expected an error, got nil")
}
})
}
}