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Implement pdfioFileSetPermissions.

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Michael R Sweet
2021-10-10 22:27:09 -04:00
parent 37e80d67b1
commit 61a7964d90
5 changed files with 249 additions and 12 deletions
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220
pdfio-file.c
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@ -1034,13 +1034,219 @@ pdfioFileSetKeywords(
}
//
// 'pdfioFileSetPermissions()' - Set the PDF permissions, encryption mode, and passwords.
//
// This function sets the PDF usage permissions, encryption mode, and
// passwords.
//
// > *Note*: This function must be called before creating or copying any
// > objects. Due to fundamental limitations in the PDF format, PDF encryption
// > offers little protection from disclosure. Permissions are not enforced in
// > any meaningful way.
//
bool // O - `true` on success, `false` otherwise
pdfioFileSetPermissions(
pdfio_file_t *pdf, // I - PDF file
pdfio_permission_t permissions, // I - Use permissions
pdfio_encryption_t encryption, // I - Type of encryption to use
const char *owner_password, // I - Owner password, if any
const char *user_password) // I - User password, if any
{
pdfio_dict_t *dict; // Encryption dictionary
size_t i, j; // Looping vars
_pdfio_md5_t md5; // MD5 context
uint8_t digest[16]; // 128-bit MD5 digest
_pdfio_rc4_t rc4; // RC4 encryption context
size_t len; // Length of password
uint8_t owner_pad[32], // Padded owner password
user_pad[32], // Padded user password
perm_bytes[4], // Permissions bytes
*file_id; // File ID bytes
size_t file_id_len; // Length of file ID
static uint8_t pad[32] = // Padding for passwords
{
0x28, 0xbf, 0x4e, 0x5e, 0x4e, 0x75, 0x8a, 0x41,
0x64, 0x00, 0x4e, 0x56, 0xff, 0xfa, 0x01, 0x08,
0x2e, 0x2e, 0x00, 0xb6, 0xd0, 0x68, 0x3e, 0x80,
0x2f, 0x0c, 0xa9, 0xfe, 0x64, 0x53, 0x69, 0x7a
};
if (!pdf)
return (false);
if (pdf->num_objs > 0)
{
_pdfioFileError(pdf, "You must call pdfioFileSetPermissions before adding any objects.");
return (false);
}
if (encryption == PDFIO_ENCRYPTION_NONE)
return (true);
if ((dict = pdfioDictCreate(pdf)) == NULL)
{
_pdfioFileError(pdf, "Unable to create encryption dictionary.");
return (false);
}
pdfioDictSetName(dict, "Filter", "Standard");
switch (encryption)
{
case PDFIO_ENCRYPTION_RC4_128 :
case PDFIO_ENCRYPTION_AES_128 :
// Create the 128-bit encryption keys...
if (user_password)
{
// Copy the user password and pad it with the special PDF pad bytes
if ((len = strlen(user_password)) > sizeof(user_pad))
len = sizeof(user_pad);
if (len > 0)
memcpy(user_pad, user_password, len);
if (len < sizeof(user_pad))
memcpy(user_pad + len, pad, sizeof(user_pad) - len);
}
else
{
// Use default (pad) password
memcpy(user_pad, pad, sizeof(user_pad));
}
if (owner_password && *owner_password)
{
// Copy the owner password and pad it with the special PDF pad bytes
if ((len = strlen(owner_password)) > sizeof(owner_pad))
len = sizeof(owner_pad);
if (len > 0)
memcpy(owner_pad, owner_password, len);
if (len < sizeof(owner_pad))
memcpy(owner_pad + len, pad, sizeof(owner_pad) - len);
}
else
{
// Generate a random owner password...
_pdfioCryptoMakeRandom(owner_pad, sizeof(owner_pad));
}
// Compute the owner key...
_pdfioCryptoMD5Init(&md5);
_pdfioCryptoMD5Append(&md5, owner_pad, 32);
_pdfioCryptoMD5Finish(&md5, digest);
// MD5 the result 50 more times...
for (i = 0; i < 50; i ++)
{
_pdfioCryptoMD5Init(&md5);
_pdfioCryptoMD5Append(&md5, digest, 16);
_pdfioCryptoMD5Finish(&md5, digest);
}
// Copy the padded user password...
memcpy(pdf->owner_key, user_pad, sizeof(pdf->owner_key));
// Encrypt the result 20 times...
for (i = 0; i < 20; i ++)
{
uint8_t encrypt_key[16];// RC4 encryption key
// XOR each byte in the digest with the loop counter to make a key...
for (j = 0; j < sizeof(encrypt_key); j ++)
encrypt_key[j] = (uint8_t)(digest[j] ^ i);
_pdfioCryptoRC4Init(&rc4, encrypt_key, sizeof(encrypt_key));
_pdfioCryptoRC4Crypt(&rc4, pdf->owner_key, sizeof(pdf->owner_key));
}
// Generate the encryption key
perm_bytes[0] = (uint8_t)permissions;
perm_bytes[1] = (uint8_t)(permissions >> 8);
perm_bytes[2] = (uint8_t)(permissions >> 16);
perm_bytes[3] = (uint8_t)(permissions >> 24);
file_id = pdfioArrayGetBinary(pdf->id_array, 0, &file_id_len);
_pdfioCryptoMD5Init(&md5);
_pdfioCryptoMD5Append(&md5, user_pad, 32);
_pdfioCryptoMD5Append(&md5, pdf->owner_key, 32);
_pdfioCryptoMD5Append(&md5, perm_bytes, 4);
_pdfioCryptoMD5Append(&md5, file_id, file_id_len);
_pdfioCryptoMD5Finish(&md5, digest);
// MD5 the result 50 times..
for (i = 0; i < 50; i ++)
{
_pdfioCryptoMD5Init(&md5);
_pdfioCryptoMD5Append(&md5, digest, 16);
_pdfioCryptoMD5Finish(&md5, digest);
}
memcpy(pdf->encryption_key, digest, 16);
// Generate the user key...
_pdfioCryptoMD5Init(&md5);
_pdfioCryptoMD5Append(&md5, pad, 32);
_pdfioCryptoMD5Append(&md5, file_id, file_id_len);
_pdfioCryptoMD5Finish(&md5, pdf->user_key);
memset(pdf->user_key + 16, 0, 16);
// Encrypt the result 20 times...
for (i = 0; i < 20; i ++)
{
// XOR each byte in the key with the loop counter...
for (j = 0; j < 16; j ++)
digest[j] = (uint8_t)(pdf->encryption_key[j] ^ i);
_pdfioCryptoRC4Init(&rc4, digest, 16);
_pdfioCryptoRC4Crypt(&rc4, pdf->user_key, sizeof(pdf->user_key));
}
// Save everything in the dictionary...
pdfioDictSetNumber(dict, "Length", 128);
pdfioDictSetBinary(dict, "O", pdf->owner_key, sizeof(pdf->owner_key));
pdfioDictSetNumber(dict, "P", (int)permissions);
pdfioDictSetNumber(dict, "R", encryption == PDFIO_ENCRYPTION_RC4_128 ? 3 : 4);
pdfioDictSetNumber(dict, "V", encryption == PDFIO_ENCRYPTION_RC4_128 ? 3 : 4);
pdfioDictSetBinary(dict, "U", pdf->user_key, sizeof(pdf->user_key));
break;
case PDFIO_ENCRYPTION_AES_256 :
// TODO: Implement AES-256 (/V 6 /R 6)
default :
_pdfioFileError(pdf, "Encryption mode %d not supported for writing.", (int)encryption);
return (false);
}
if ((pdf->encrypt_obj = pdfioFileCreateObj(pdf, dict)) == NULL)
{
_pdfioFileError(pdf, "Unable to create encryption object.");
return (false);
}
pdfioObjClose(pdf->encrypt_obj);
pdf->encryption = encryption;
pdf->permissions = permissions;
return (true);
}
//
// 'pdfioFileSetSubject()' - Set the subject for a PDF file.
//
void
pdfioFileSetSubject(pdfio_file_t *pdf, // I - PDF file
const char *value)// I - Value
pdfioFileSetSubject(
pdfio_file_t *pdf, // I - PDF file
const char *value) // I - Value
{
if (pdf && pdf->info)
pdfioDictSetString(pdf->info->value.value.dict, "Subject", pdfioStringCreate(pdf, value));
@ -1702,9 +1908,9 @@ load_xref(pdfio_file_t *pdf, // I - PDF file
PDFIO_DEBUG("load_xref: Root=%p(%lu)\n", pdf->root, (unsigned long)pdf->root->number);
pdf->info = pdfioDictGetObj(pdf->trailer, "Info");
pdf->encrypt = pdfioDictGetObj(pdf->trailer, "Encrypt");
pdf->id_array = pdfioDictGetArray(pdf->trailer, "ID");
pdf->info = pdfioDictGetObj(pdf->trailer, "Info");
pdf->encrypt_obj = pdfioDictGetObj(pdf->trailer, "Encrypt");
pdf->id_array = pdfioDictGetArray(pdf->trailer, "ID");
return (load_pages(pdf, pdfioDictGetObj(pdfioObjGetDict(pdf->root), "Pages")));
}
@ -1819,8 +2025,8 @@ write_trailer(pdfio_file_t *pdf) // I - PDF file
goto done;
}
if (pdf->encrypt)
pdfioDictSetObj(pdf->trailer, "Encrypt", pdf->encrypt);
if (pdf->encrypt_obj)
pdfioDictSetObj(pdf->trailer, "Encrypt", pdf->encrypt_obj);
if (pdf->id_array)
pdfioDictSetArray(pdf->trailer, "ID", pdf->id_array);
pdfioDictSetObj(pdf->trailer, "Info", pdf->info);