hardcoresushi/libcryfs
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Add a padding step between inner encryption and outer encryption to hide the size of the cipher name that is added inbetween

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This commit is contained in:
Sebastian Messmer 2015-10-27 19:00:24 +01:00
parent 08e4ae8a2e
commit 5a73042c63
3 changed files with 12 additions and 5 deletions
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2
src/config/crypto/ConcreteInnerEncryptor.h
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@ -13,7 +13,7 @@ namespace cryfs {
template<class Cipher> template<class Cipher>
class ConcreteInnerEncryptor: public InnerEncryptor { class ConcreteInnerEncryptor: public InnerEncryptor {
public: public:
static constexpr size_t CONFIG_SIZE = 512; // Config data is grown to this size before encryption to hide its actual size static constexpr size_t CONFIG_SIZE = 512; // Inner config data is grown to this size before encryption to hide its actual size
ConcreteInnerEncryptor(typename Cipher::EncryptionKey key, const std::string &cipherName); ConcreteInnerEncryptor(typename Cipher::EncryptionKey key, const std::string &cipherName);

14
src/config/crypto/CryConfigEncryptor.cpp
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@ -1,4 +1,5 @@
#include "CryConfigEncryptor.h" #include "CryConfigEncryptor.h"
#include "RandomPadding.h"
using std::string; using std::string;
using cpputils::Deserializer; using cpputils::Deserializer;
@ -29,7 +30,8 @@ namespace cryfs {
Data CryConfigEncryptor::encrypt(const Data &plaintext) { Data CryConfigEncryptor::encrypt(const Data &plaintext) {
auto inner = _innerEncryptor->encrypt(plaintext); auto inner = _innerEncryptor->encrypt(plaintext);
auto ciphertext = OuterCipher::encrypt(static_cast<const uint8_t*>(inner.data()), inner.size(), _outerKey); auto padded = RandomPadding::add(inner, CONFIG_SIZE);
auto ciphertext = OuterCipher::encrypt(static_cast<const uint8_t*>(padded.data()), padded.size(), _outerKey);
return _serialize(ciphertext); return _serialize(ciphertext);
} }
@ -53,9 +55,9 @@ namespace cryfs {
try { try {
checkHeader(&deserializer); checkHeader(&deserializer);
_ignoreKey(&deserializer); _ignoreKey(&deserializer);
auto configData = _loadAndDecryptConfigData(&deserializer); auto result = _loadAndDecryptConfigData(&deserializer);
deserializer.finished(); deserializer.finished();
return configData; return result;
} catch (const std::exception &e) { } catch (const std::exception &e) {
LOG(ERROR) << "Error loading configuration: " << e.what(); LOG(ERROR) << "Error loading configuration: " << e.what();
return boost::none; // This can be caused by invalid loaded data and is not necessarily a programming logic error. Don't throw exception. return boost::none; // This can be caused by invalid loaded data and is not necessarily a programming logic error. Don't throw exception.
@ -72,6 +74,10 @@ namespace cryfs {
if(inner == none) { if(inner == none) {
return none; return none;
} }
return _innerEncryptor->decrypt(*inner); auto depadded = RandomPadding::remove(*inner);
if(depadded == none) {
return none;
}
return _innerEncryptor->decrypt(*depadded);
} }
} }

1
src/config/crypto/CryConfigEncryptor.h
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@ -17,6 +17,7 @@ namespace cryfs {
class CryConfigEncryptor { class CryConfigEncryptor {
public: public:
using OuterCipher = blockstore::encrypted::AES256_GCM; using OuterCipher = blockstore::encrypted::AES256_GCM;
static constexpr size_t CONFIG_SIZE = 1024; // Config data is grown to this size before encryption to hide its actual size
CryConfigEncryptor(cpputils::unique_ref<InnerEncryptor> innerEncryptor, OuterCipher::EncryptionKey outerKey, DerivedKeyConfig keyConfig); CryConfigEncryptor(cpputils::unique_ref<InnerEncryptor> innerEncryptor, OuterCipher::EncryptionKey outerKey, DerivedKeyConfig keyConfig);