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Support per-object file IDs (Issue #42)

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Michael R Sweet 2023-12-12 21:48:58 -05:00
parent f4aa951165
commit 2b92044504
No known key found for this signature in database
GPG Key ID: BE67C75EC81F3244
3 changed files with 67 additions and 12 deletions
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1
CHANGES.md
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@ -15,6 +15,7 @@ v1.2.0 (Month DD, YYYY)
- Updated the token reading code to protect against some obvious abuses of the
PDF format.
- Updated the xref reading code to protect against loops.
- Fixed handling of encrypted PDFs with per-object file IDs (Issue #42)
- Fixed handling of of trailer dictionaries that started immediately after the
"trailer" keyword (Issue #58)
- Fixed handling of invalid, but common, PDF files with a generation number of

75
pdfio-crypto.c
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@ -406,9 +406,14 @@ _pdfio_crypto_cb_t // O - Decryption callback or `NULL` for none
uint8_t *iv, // I - Buffer for initialization vector
size_t *ivlen) // IO - Size of initialization vector
{
uint8_t data[21]; /* Key data */
_pdfio_md5_t md5; /* MD5 state */
uint8_t digest[16]; /* MD5 digest value */
uint8_t data[21]; // Key data
_pdfio_md5_t md5; // MD5 state
uint8_t digest[16]; // MD5 digest value
pdfio_array_t *id_array; // Object ID array
unsigned char *id_value; // Object ID value
size_t id_len; // Length of object ID
uint8_t *file_key, // Computed file key to use
temp_key[16]; // File key for object
PDFIO_DEBUG("_pdfioCryptoMakeReader(pdf=%p, obj=%p(%d), ctx=%p, iv=%p, ivlen=%p(%d))\n", pdf, obj, (int)obj->number, ctx, iv, ivlen, (int)*ivlen);
@ -420,6 +425,53 @@ _pdfio_crypto_cb_t // O - Decryption callback or `NULL` for none
return (NULL);
}
if ((id_array = pdfioDictGetArray(pdfioObjGetDict(obj), "ID")) != NULL)
{
// Object has its own ID that will get used for encryption...
_pdfio_md5_t md5; // MD5 context
uint8_t file_digest[16]; // MD5 digest of file ID and pad
uint8_t user_pad[32], // Padded user password
own_user_key[32], // Calculated user key
pdf_user_key[32]; // Decrypted user key
if ((id_value = pdfioArrayGetBinary(id_array, 0, &id_len)) == NULL)
{
*ivlen = 0;
return (NULL);
}
_pdfioCryptoMD5Init(&md5);
_pdfioCryptoMD5Append(&md5, pdf_passpad, 32);
_pdfioCryptoMD5Append(&md5, id_value, id_len);
_pdfioCryptoMD5Finish(&md5, file_digest);
make_owner_key(pdf->encryption, pdf->password, pdf->owner_key, user_pad);
make_file_key(pdf->encryption, pdf->permissions, id_value, id_len, user_pad, pdf->owner_key, temp_key);
make_user_key(id_value, id_len, own_user_key);
if (memcmp(own_user_key, pdf->user_key, sizeof(own_user_key)))
{
make_file_key(pdf->encryption, pdf->permissions, id_value, id_len, pdf->password, pdf->owner_key, temp_key);
make_user_key(id_value, id_len, own_user_key);
memcpy(pdf_user_key, pdf->user_key, sizeof(pdf_user_key));
decrypt_user_key(pdf->encryption, temp_key, pdf_user_key);
if (memcmp(pdf->password, pdf_user_key, 32) && memcmp(own_user_key, pdf_user_key, 16))
{
*ivlen = 0;
return (NULL);
}
}
file_key = temp_key;
}
else
{
// Use the default file key...
file_key = pdf->file_key;
}
switch (pdf->encryption)
{
default :
@ -428,7 +480,7 @@ _pdfio_crypto_cb_t // O - Decryption callback or `NULL` for none
case PDFIO_ENCRYPTION_RC4_40 :
// Copy the key data for the MD5 hash.
memcpy(data, pdf->file_key, sizeof(pdf->file_key));
memcpy(data, file_key, 16);
data[16] = (uint8_t)obj->number;
data[17] = (uint8_t)(obj->number >> 8);
data[18] = (uint8_t)(obj->number >> 16);
@ -455,7 +507,7 @@ _pdfio_crypto_cb_t // O - Decryption callback or `NULL` for none
case PDFIO_ENCRYPTION_RC4_128 :
// Copy the key data for the MD5 hash.
memcpy(data, pdf->file_key, sizeof(pdf->file_key));
memcpy(data, file_key, 16);
data[16] = (uint8_t)obj->number;
data[17] = (uint8_t)(obj->number >> 8);
data[18] = (uint8_t)(obj->number >> 16);
@ -769,17 +821,16 @@ _pdfioCryptoUnlock(
{
// Matches!
memcpy(pdf->file_key, file_key, sizeof(pdf->file_key));
memcpy(pdf->password, pad, sizeof(pdf->password));
return (true);
}
/*
* Not the owner password, try the user password...
*/
// Not the owner password, try the user password...
make_file_key(pdf->encryption, pdf->permissions, file_id, file_idlen, pad, pdf->owner_key, file_key);
PDFIO_DEBUG("_pdfioCryptoUnlock: Fuse=%02X%02X%02X%02X...%02X%02X%02X%02X\n", file_key[0], file_key[1], file_key[2], file_key[3], file_key[12], file_key[13], file_key[14], file_key[15]);
make_user_key(file_id, file_idlen, user_key);
make_user_key(file_id, file_idlen, own_user_key);
memcpy(pdf_user_key, pdf->user_key, sizeof(pdf_user_key));
decrypt_user_key(pdf->encryption, file_key, pdf_user_key);
@ -787,10 +838,12 @@ _pdfioCryptoUnlock(
PDFIO_DEBUG("_pdfioCryptoUnlock: Uuse=%02X%02X%02X%02X...%02X%02X%02X%02X\n", user_key[0], user_key[1], user_key[2], user_key[3], user_key[28], user_key[29], user_key[30], user_key[31]);
PDFIO_DEBUG("_pdfioCryptoUnlock: Updf=%02X%02X%02X%02X...%02X%02X%02X%02X\n", pdf_user_key[0], pdf_user_key[1], pdf_user_key[2], pdf_user_key[3], pdf_user_key[28], pdf_user_key[29], pdf_user_key[30], pdf_user_key[31]);
if (!memcmp(pad, pdf_user_key, 32) || !memcmp(user_key, pdf_user_key, 16))
if (!memcmp(pad, pdf_user_key, 32) || !memcmp(own_user_key, pdf_user_key, 16))
{
// Matches!
memcpy(pdf->file_key, file_key, sizeof(pdf->file_key));
memcpy(pdf->password, pad, sizeof(pdf->password));
return (true);
}
}

3
pdfio-private.h
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@ -237,7 +237,8 @@ struct _pdfio_file_s // PDF file structure
pdfio_permission_t permissions; // Access permissions (encrypted PDF files)
uint8_t file_key[16], // File encryption key
owner_key[32], // Owner encryption key
user_key[32]; // User encryption key
user_key[32], // User encryption key
password[32]; // Padded password
size_t file_keylen, // Length of file encryption key
owner_keylen, // Length of owner encryption key
user_keylen; // Length of user encryption key