Implement an mlock()'d string class for storing passphrases

SecureString is identical to std::string except with secure_allocator
substituting for std::allocator. This makes casting between them
impossible, so converting between the two at API boundaries requires
calling ::c_str() for now.

3 files changed, 14 insertions, 12 deletions

diff --git a/src/qt/askpassphrasedialog.cpp b/src/qt/askpassphrasedialog.cpp
index b52acf4545..4ee67e7c87 100644
--- a/src/qt/askpassphrasedialog.cpp
+++ b/src/qt/askpassphrasedialog.cpp
@@ -70,16 +70,17 @@ void AskPassphraseDialog::setModel(WalletModel *model)
 
 void AskPassphraseDialog::accept()
 {
-    std::string oldpass, newpass1, newpass2;
+    SecureString oldpass, newpass1, newpass2;
     if(!model)
         return;
-    // TODO: mlock memory / munlock on return so they will not be swapped out, really need "mlockedstring" wrapper class to do this safely
     oldpass.reserve(MAX_PASSPHRASE_SIZE);
     newpass1.reserve(MAX_PASSPHRASE_SIZE);
     newpass2.reserve(MAX_PASSPHRASE_SIZE);
-    oldpass.assign(ui->passEdit1->text().toStdString());
-    newpass1.assign(ui->passEdit2->text().toStdString());
-    newpass2.assign(ui->passEdit3->text().toStdString());
+    // TODO: get rid of this .c_str() by implementing SecureString::operator=(std::string)
+    // Alternately, find a way to make this input mlock()'d to begin with.
+    oldpass.assign(ui->passEdit1->text().toStdString().c_str());
+    newpass1.assign(ui->passEdit2->text().toStdString().c_str());
+    newpass2.assign(ui->passEdit3->text().toStdString().c_str());
 
     switch(mode)
     {
diff --git a/src/qt/walletmodel.cpp b/src/qt/walletmodel.cpp
index 2f989661f0..f028f10f6c 100644
--- a/src/qt/walletmodel.cpp
+++ b/src/qt/walletmodel.cpp
@@ -200,7 +200,7 @@ WalletModel::EncryptionStatus WalletModel::getEncryptionStatus() const
     }
 }
 
-bool WalletModel::setWalletEncrypted(bool encrypted, const std::string &passphrase)
+bool WalletModel::setWalletEncrypted(bool encrypted, const SecureString &passphrase)
 {
     if(encrypted)
     {
@@ -214,7 +214,7 @@ bool WalletModel::setWalletEncrypted(bool encrypted, const std::string &passphra
     }
 }
 
-bool WalletModel::setWalletLocked(bool locked, const std::string &passPhrase)
+bool WalletModel::setWalletLocked(bool locked, const SecureString &passPhrase)
 {
     if(locked)
     {
@@ -228,7 +228,7 @@ bool WalletModel::setWalletLocked(bool locked, const std::string &passPhrase)
     }
 }
 
-bool WalletModel::changePassphrase(const std::string &oldPass, const std::string &newPass)
+bool WalletModel::changePassphrase(const SecureString &oldPass, const SecureString &newPass)
 {
     bool retval;
     CRITICAL_BLOCK(wallet->cs_wallet)
diff --git a/src/qt/walletmodel.h b/src/qt/walletmodel.h
index b7b6973b3b..055ba184b0 100644
--- a/src/qt/walletmodel.h
+++ b/src/qt/walletmodel.h
@@ -2,7 +2,8 @@
 #define WALLETMODEL_H
 
 #include <QObject>
-#include <string>
+
+#include "util.h"
 
 class OptionsModel;
 class AddressTableModel;
@@ -72,10 +73,10 @@ public:
     SendCoinsReturn sendCoins(const QList<SendCoinsRecipient> &recipients);
 
     // Wallet encryption
-    bool setWalletEncrypted(bool encrypted, const std::string &passphrase);
+    bool setWalletEncrypted(bool encrypted, const SecureString &passphrase);
     // Passphrase only needed when unlocking
-    bool setWalletLocked(bool locked, const std::string &passPhrase=std::string());
-    bool changePassphrase(const std::string &oldPass, const std::string &newPass);
+    bool setWalletLocked(bool locked, const SecureString &passPhrase=SecureString());
+    bool changePassphrase(const SecureString &oldPass, const SecureString &newPass);
 
     // RAI object for unlocking wallet, returned by requestUnlock()
     class UnlockContext