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Diffstat (limited to 'libqpdf/QPDF_encryption.cc')
| -rw-r--r-- | libqpdf/QPDF_encryption.cc | 441 |
1 files changed, 441 insertions, 0 deletions
diff --git a/libqpdf/QPDF_encryption.cc b/libqpdf/QPDF_encryption.cc new file mode 100644 index 00000000..e5e2d8be --- /dev/null +++ b/libqpdf/QPDF_encryption.cc @@ -0,0 +1,441 @@ +// This file implements methods from the QPDF class that involve +// encryption. + +#include <qpdf/QPDF.hh> + +#include <qpdf/QPDFExc.hh> + +#include <qpdf/QUtil.hh> +#include <qpdf/Pl_RC4.hh> +#include <qpdf/RC4.hh> +#include <qpdf/MD5.hh> + +static char const padding_string[] = { + 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 +}; + +static unsigned int const O_key_bytes = sizeof(MD5::Digest); +static unsigned int const id_bytes = 16; +static unsigned int const key_bytes = 32; + +void +pad_or_truncate_password(std::string const& password, char k1[key_bytes]) +{ + int password_bytes = std::min(key_bytes, password.length()); + int pad_bytes = key_bytes - password_bytes; + memcpy(k1, password.c_str(), password_bytes); + memcpy(k1 + password_bytes, padding_string, pad_bytes); +} + +void +QPDF::trim_user_password(std::string& user_password) +{ + // Although unnecessary, this routine trims the padding string + // from the end of a user password. Its only purpose is for + // recovery of user passwords which is done in the test suite. + char const* cstr = user_password.c_str(); + size_t len = user_password.length(); + if (len < key_bytes) + { + return; + } + + char* p = 0; + while ((p = strchr(cstr, '\x28')) != 0) + { + if (memcmp(p, padding_string, len - (p - cstr)) == 0) + { + user_password = user_password.substr(0, p - cstr); + return; + } + } +} + +static std::string +pad_or_truncate_password(std::string const& password) +{ + char k1[key_bytes]; + pad_or_truncate_password(password, k1); + return std::string(k1, key_bytes); +} + +static void +iterate_md5_digest(MD5& md5, MD5::Digest& digest, int iterations) +{ + md5.digest(digest); + + for (int i = 0; i < iterations; ++i) + { + MD5 m; + m.encodeDataIncrementally((char*)digest, sizeof(digest)); + m.digest(digest); + } +} + + +static void +iterate_rc4(unsigned char* data, int data_len, + unsigned char* okey, int key_len, + int iterations, bool reverse) +{ + unsigned char* key = new unsigned char[key_len]; + for (int i = 0; i < iterations; ++i) + { + int const xor_value = (reverse ? iterations - 1 - i : i); + for (int j = 0; j < key_len; ++j) + { + key[j] = okey[j] ^ xor_value; + } + RC4 rc4(key, key_len); + rc4.process(data, data_len); + } + delete [] key; +} + +std::string +QPDF::compute_data_key(std::string const& encryption_key, + int objid, int generation) +{ + // Algorithm 3.1 from the PDF 1.4 Reference Manual + + std::string result = encryption_key; + + // Append low three bytes of object ID and low two bytes of generation + result += (char) (objid & 0xff); + result += (char) ((objid >> 8) & 0xff); + result += (char) ((objid >> 16) & 0xff); + result += (char) (generation & 0xff); + result += (char) ((generation >> 8) & 0xff); + + MD5 md5; + md5.encodeDataIncrementally(result.c_str(), result.length()); + MD5::Digest digest; + md5.digest(digest); + return std::string((char*) digest, + std::min(result.length(), (size_t) 16)); +} + +std::string +QPDF::compute_encryption_key( + std::string const& password, EncryptionData const& data) +{ + // Algorithm 3.2 from the PDF 1.4 Reference Manual + + MD5 md5; + md5.encodeDataIncrementally( + pad_or_truncate_password(password).c_str(), key_bytes); + md5.encodeDataIncrementally(data.O.c_str(), key_bytes); + char pbytes[4]; + pbytes[0] = (char) (data.P & 0xff); + pbytes[1] = (char) ((data.P >> 8) & 0xff); + pbytes[2] = (char) ((data.P >> 16) & 0xff); + pbytes[3] = (char) ((data.P >> 24) & 0xff); + md5.encodeDataIncrementally(pbytes, 4); + md5.encodeDataIncrementally(data.id1.c_str(), id_bytes); + MD5::Digest digest; + iterate_md5_digest(md5, digest, ((data.R == 3) ? 50 : 0)); + return std::string((char*)digest, data.Length_bytes); +} + +static void +compute_O_rc4_key(std::string const& user_password, + std::string const& owner_password, + QPDF::EncryptionData const& data, + unsigned char key[O_key_bytes]) +{ + std::string password = owner_password; + if (password.empty()) + { + password = user_password; + } + MD5 md5; + md5.encodeDataIncrementally( + pad_or_truncate_password(password).c_str(), key_bytes); + MD5::Digest digest; + iterate_md5_digest(md5, digest, ((data.R == 3) ? 50 : 0)); + memcpy(key, digest, O_key_bytes); +} + +static std::string +compute_O_value(std::string const& user_password, + std::string const& owner_password, + QPDF::EncryptionData const& data) +{ + // Algorithm 3.3 from the PDF 1.4 Reference Manual + + unsigned char O_key[O_key_bytes]; + compute_O_rc4_key(user_password, owner_password, data, O_key); + + char upass[key_bytes]; + pad_or_truncate_password(user_password, upass); + iterate_rc4((unsigned char*) upass, key_bytes, + O_key, data.Length_bytes, (data.R == 3) ? 20 : 1, false); + return std::string(upass, key_bytes); +} + +static +std::string +compute_U_value_R2(std::string const& user_password, + QPDF::EncryptionData const& data) +{ + // Algorithm 3.4 from the PDF 1.4 Reference Manual + + std::string k1 = QPDF::compute_encryption_key(user_password, data); + char udata[key_bytes]; + pad_or_truncate_password("", udata); + iterate_rc4((unsigned char*) udata, key_bytes, + (unsigned char*)k1.c_str(), data.Length_bytes, 1, false); + return std::string(udata, key_bytes); +} + +static +std::string +compute_U_value_R3(std::string const& user_password, + QPDF::EncryptionData const& data) +{ + // Algorithm 3.5 from the PDF 1.4 Reference Manual + + std::string k1 = QPDF::compute_encryption_key(user_password, data); + MD5 md5; + md5.encodeDataIncrementally( + pad_or_truncate_password("").c_str(), key_bytes); + md5.encodeDataIncrementally(data.id1.c_str(), data.id1.length()); + MD5::Digest digest; + md5.digest(digest); + iterate_rc4(digest, sizeof(MD5::Digest), + (unsigned char*) k1.c_str(), data.Length_bytes, 20, false); + char result[key_bytes]; + memcpy(result, digest, sizeof(MD5::Digest)); + // pad with arbitrary data -- make it consistent for the sake of + // testing + for (unsigned int i = sizeof(MD5::Digest); i < key_bytes; ++i) + { + result[i] = (char)((i * i) % 0xff); + } + return std::string(result, key_bytes); +} + +static std::string +compute_U_value(std::string const& user_password, + QPDF::EncryptionData const& data) +{ + if (data.R == 3) + { + return compute_U_value_R3(user_password, data); + } + + return compute_U_value_R2(user_password, data); +} + +static bool +check_user_password(std::string const& user_password, + QPDF::EncryptionData const& data) +{ + // Algorithm 3.6 from the PDF 1.4 Reference Manual + + std::string u_value = compute_U_value(user_password, data); + int to_compare = ((data.R == 3) ? sizeof(MD5::Digest) : key_bytes); + return (memcmp(data.U.c_str(), u_value.c_str(), to_compare) == 0); +} + +static bool +check_owner_password(std::string& user_password, + std::string const& owner_password, + QPDF::EncryptionData const& data) +{ + // Algorithm 3.7 from the PDF 1.4 Reference Manual + + unsigned char key[O_key_bytes]; + compute_O_rc4_key(user_password, owner_password, data, key); + unsigned char O_data[key_bytes]; + memcpy(O_data, (unsigned char*) data.O.c_str(), key_bytes); + iterate_rc4(O_data, key_bytes, key, data.Length_bytes, + (data.R == 3) ? 20 : 1, true); + std::string new_user_password = + std::string((char*)O_data, key_bytes); + bool result = false; + if (check_user_password(new_user_password, data)) + { + result = true; + user_password = new_user_password; + } + return result; +} + +void +QPDF::initializeEncryption() +{ + if (this->encryption_initialized) + { + return; + } + this->encryption_initialized = true; + + // After we initialize encryption parameters, we must used stored + // key information and never look at /Encrypt again. Otherwise, + // things could go wrong if someone mutates the encryption + // dictionary. + + if (! this->trailer.hasKey("/Encrypt")) + { + return; + } + + QPDFObjectHandle id_obj = this->trailer.getKey("/ID"); + if (! (id_obj.isArray() && + (id_obj.getArrayNItems() == 2) && + id_obj.getArrayItem(0).isString())) + { + throw QPDFExc(this->file.getName(), this->file.getLastOffset(), + "invalid /ID in trailer dictionary"); + } + + std::string id1 = id_obj.getArrayItem(0).getStringValue(); + if (id1.length() != id_bytes) + { + throw QPDFExc(this->file.getName(), this->file.getLastOffset(), + "first /ID string in trailer dictionary has " + "incorrect length"); + } + + QPDFObjectHandle encryption_dict = this->trailer.getKey("/Encrypt"); + if (! encryption_dict.isDictionary()) + { + throw QPDFExc(this->file.getName(), this->file.getLastOffset(), + "/Encrypt in trailer dictionary is not a dictionary"); + } + + if (! (encryption_dict.getKey("/Filter").isName() && + (encryption_dict.getKey("/Filter").getName() == "/Standard"))) + { + throw QPDFExc(this->file.getName(), this->file.getLastOffset(), + "unsupported encryption filter"); + } + + if (! (encryption_dict.getKey("/V").isInteger() && + encryption_dict.getKey("/R").isInteger() && + encryption_dict.getKey("/O").isString() && + encryption_dict.getKey("/U").isString() && + encryption_dict.getKey("/P").isInteger())) + { + throw QPDFExc(this->file.getName(), this->file.getLastOffset(), + "some encryption dictionary parameters are missing " + "or the wrong type"); + } + + int V = encryption_dict.getKey("/V").getIntValue(); + int R = encryption_dict.getKey("/R").getIntValue(); + std::string O = encryption_dict.getKey("/O").getStringValue(); + std::string U = encryption_dict.getKey("/U").getStringValue(); + unsigned int P = (unsigned int) encryption_dict.getKey("/P").getIntValue(); + + if (! (((R == 2) || (R == 3)) && + ((V == 1) || (V == 2)))) + { + throw QPDFExc(this->file.getName(), this->file.getLastOffset(), + "Unsupported /R or /V in encryption dictionary"); + } + + if (! ((O.length() == key_bytes) && (U.length() == key_bytes))) + { + throw QPDFExc(this->file.getName(), this->file.getLastOffset(), + "incorrect length for /O and/or /P in " + "encryption dictionary"); + } + + int Length = 40; + if (encryption_dict.getKey("/Length").isInteger()) + { + Length = encryption_dict.getKey("/Length").getIntValue(); + if ((Length % 8) || (Length < 40) || (Length > 128)) + { + throw QPDFExc(this->file.getName(), this->file.getLastOffset(), + "invalid /Length value in encryption dictionary"); + } + } + + EncryptionData data(V, R, Length / 8, P, O, U, id1); + if (check_owner_password(this->user_password, this->provided_password, data)) + { + // password supplied was owner password; user_password has + // been initialized + } + else if (check_user_password(this->provided_password, data)) + { + this->user_password = this->provided_password; + } + else + { + throw QPDFExc(this->file.getName() + ": invalid password"); + } + + this->encrypted = true; + this->encryption_key = compute_encryption_key(this->user_password, data); +} + +std::string +QPDF::getKeyForObject(int objid, int generation) +{ + if (! this->encrypted) + { + throw QEXC::Internal("request for encryption key in non-encrypted PDF"); + } + + if (! ((objid == this->cached_key_objid) && + (generation == this->cached_key_generation))) + { + this->cached_object_encryption_key = + compute_data_key(this->encryption_key, objid, generation); + this->cached_key_objid = objid; + this->cached_key_generation = generation; + } + + return this->cached_object_encryption_key; +} + +void +QPDF::decryptString(std::string& str, int objid, int generation) +{ + if (objid == 0) + { + return; + } + std::string key = getKeyForObject(objid, generation); + char* tmp = QUtil::copy_string(str); + unsigned int vlen = str.length(); + RC4 rc4((unsigned char const*)key.c_str(), key.length()); + rc4.process((unsigned char*)tmp, vlen); + str = std::string(tmp, vlen); + delete [] tmp; +} + +void +QPDF::decryptStream(Pipeline*& pipeline, int objid, int generation, + std::vector<PointerHolder<Pipeline> >& heap) +{ + std::string key = getKeyForObject(objid, generation); + pipeline = new Pl_RC4("stream decryption", pipeline, + (unsigned char*) key.c_str(), key.length()); + heap.push_back(pipeline); +} + +void +QPDF::compute_encryption_O_U( + char const* user_password, char const* owner_password, + int V, int R, int key_len, unsigned long P, + std::string const& id1, std::string& O, std::string& U) +{ + EncryptionData data(V, R, key_len, P, "", "", id1); + data.O = compute_O_value(user_password, owner_password, data); + O = data.O; + U = compute_U_value(user_password, data); +} + +std::string const& +QPDF::getUserPassword() const +{ + return this->user_password; +} |