Add method to import seed when creating a wallet.

This only adds the dialog and will call the CreateNewWallet RPC with
the decoded seed rather than a randomly-generated one.

As btcwallet does not support recovering addresses and transactions
for an imported seed, this feature won't work correctly and
transaction history will have to be recovered after generating the
same number of addresses used from the previous wallet.  However, once
that is implemented, this GUI feature should work as intended.

The seed can be inputed using either hex or the PGP word list
encoding.  At the moment, no checksumming is used or removed from the
input, and all bytes are considered part of the seed.  If any
additional data is added to a seed encoding later, the
WalletSeed.DecodeAndValidateUserInput method will need to be changed
to interpret this separately.

Closes #24.

Paymetheus.Bitcoin/Paymetheus.Bitcoin.csproj

@@ -80,6 +80,7 @@
     <Compile Include="Wallet\UnspentOutput.cs" />
     <Compile Include="Wallet\Wallet.cs" />
     <Compile Include="Wallet\WalletChanges.cs" />
+    <Compile Include="Wallet\WalletSeed.cs" />
     <Compile Include="Wallet\WalletTransaction.cs" />
   </ItemGroup>
   <ItemGroup>

Paymetheus.Bitcoin/Util/Hexadecimal.cs

@@ -12,7 +12,7 @@ public static byte[] Decode(string value)
         {
             byte[] result;
             if (!TryDecode(value, out result))
-                throw new Exception("Value is not a valid hexadecimal string");
+                throw new HexadecimalEncodingException();
             return result;
         }
 
@@ -72,4 +72,9 @@ public static string Encode(byte[] bytes)
             return s.ToString();
         }
     }
+
+    public class HexadecimalEncodingException : Exception
+    {
+        public HexadecimalEncodingException() : base("Value is not a valid hexadecimal string") { }
+    }
 }

Paymetheus.Bitcoin/Wallet/Wallet.cs

@@ -4,7 +4,6 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using System.Security.Cryptography;
 
 namespace Paymetheus.Bitcoin.Wallet
 {
@@ -28,11 +27,6 @@ public sealed class Wallet
         /// </summary>
         public const int MinRecentTransactions = 10;
 
-        /// <summary>
-        /// The length in bytes of the wallet's BIP0032 seed.
-        /// </summary>
-        public const int SeedLength = 32;
-
         public Wallet(BlockChainIdentity activeChain, TransactionSet txSet, Dictionary<Account, AccountProperties> accounts, BlockIdentity chainTip)
         {
             if (activeChain == null)
@@ -328,15 +322,5 @@ public string OutputDestination(WalletTransaction.Output output)
         public string AccountName(Account account) => _accounts[account].AccountName;
 
         public IEnumerable<KeyValuePair<Account, AccountProperties>> EnumrateAccounts() => _accounts;
-
-        public static byte[] RandomSeed()
-        {
-            var seed = new byte[SeedLength];
-            using (var prng = new RNGCryptoServiceProvider())
-            {
-                prng.GetBytes(seed);
-            }
-            return seed;
-        }
     }
 }

Paymetheus.Bitcoin/Wallet/WalletSeed.cs

@@ -0,0 +1,62 @@
+// Copyright (c) 2016 The btcsuite developers
+// Licensed under the ISC license.  See LICENSE file in the project root for full license information.
+
+using Paymetheus.Bitcoin.Util;
+using System;
+using System.Security.Cryptography;
+
+namespace Paymetheus.Bitcoin.Wallet
+{
+    public static class WalletSeed
+    {
+        /// <summary>
+        /// The length in bytes of the wallet's BIP0032 seed.
+        /// </summary>
+        public const int SeedLength = 32;
+
+        public static byte[] GenerateRandomSeed()
+        {
+            var seed = new byte[SeedLength];
+            using (var prng = new RNGCryptoServiceProvider())
+            {
+                prng.GetBytes(seed);
+            }
+            return seed;
+        }
+
+        /// <summary>
+        /// Decodes user input as either the hexadecimal or PGP word list encoding
+        /// of a seed and validates the seed length.
+        /// </summary>
+        public static byte[] DecodeAndValidateUserInput(string userInput, PgpWordList pgpWordList)
+        {
+            if (userInput == null)
+                throw new ArgumentNullException(nameof(userInput));
+            if (pgpWordList == null)
+                throw new ArgumentNullException(nameof(pgpWordList));
+
+            var decodedInput = DecodeUserInput(userInput, pgpWordList);
+            if (decodedInput.Length != SeedLength)
+            {
+                throw new Exception($"Decoded seed must have byte length {SeedLength}");
+            }
+            return decodedInput;
+        }
+
+        private static byte[] DecodeUserInput(string userInput, PgpWordList pgpWordList)
+        {
+            byte[] seed;
+            if (Hexadecimal.TryDecode(userInput, out seed))
+                return seed;
+
+            var splitInput = userInput.Split(new char[0], StringSplitOptions.RemoveEmptyEntries);
+            if (splitInput.Length == 1)
+            {
+                // Hex decoding failed, but it's not a multi-word mneumonic either.
+                // Assume the user intended hex.
+                throw new HexadecimalEncodingException();
+            }
+            return pgpWordList.Decode(splitInput);
+        }
+    }
+}

Paymetheus/BindingProperties.cs

@@ -0,0 +1,54 @@
+// Copyright (c) 2016 The btcsuite developers
+// Licensed under the ISC license.  See LICENSE file in the project root for full license information.
+
+using System.Windows;
+using System.Windows.Data;
+using System.Windows.Input;
+
+namespace Paymetheus
+{
+    static class BindingProperties
+    {
+        public static readonly DependencyProperty UpdateSourceOnEnterProperty =
+            DependencyProperty.RegisterAttached(nameof(UpdateSourceOnEnter), typeof(DependencyProperty),
+                typeof(BindingProperties), new PropertyMetadata(null, UpdateSourceOnEnter));
+
+        public static DependencyProperty GetUpdateSourceOnEnterProperty(DependencyObject instance)
+        {
+            return (DependencyProperty)instance.GetValue(UpdateSourceOnEnterProperty);
+        }
+
+        public static void SetUpdateSourceOnEnterProperty(DependencyObject instance, DependencyProperty value)
+        {
+            instance.SetValue(UpdateSourceOnEnterProperty, value);
+        }
+
+        private static void UpdateSourceOnEnter(DependencyObject dp, DependencyPropertyChangedEventArgs e)
+        {
+            var element = dp as UIElement;
+            if (element == null)
+                return;
+
+            if (e.OldValue != null)
+                element.PreviewKeyDown -= UpdateSourceOnEnter_PreviewKeyDown;
+            if (e.NewValue != null)
+                element.PreviewKeyDown += UpdateSourceOnEnter_PreviewKeyDown;
+        }
+
+        private static void UpdateSourceOnEnter_PreviewKeyDown(object sender, KeyEventArgs e)
+        {
+            if (e.Key == Key.Enter)
+            {
+                var element = sender as UIElement;
+                if (element == null)
+                    return;
+
+                var property = GetUpdateSourceOnEnterProperty(element);
+                if (property == null)
+                    return;
+
+                BindingOperations.GetBindingExpression(element, property)?.UpdateSource();
+            }
+        }
+    }
+}

Paymetheus/ConnectionWizardView.xaml

@@ -10,8 +10,8 @@
         <DataTemplate DataType="{x:Type local:ConsensusServerRpcConnectionDialog}">
             <local:ConsensusServerConnectionOptionsView/>
         </DataTemplate>
-        <DataTemplate DataType="{x:Type local:DisplaySeedDialog}">
-            <local:DisplaySeedView/>
+        <DataTemplate DataType="{x:Type local:CreateOrImportSeedDialog}">
+            <local:CreateOrImportSeedView/>
         </DataTemplate>
         <DataTemplate DataType="{x:Type local:PromptPublicPassphraseDialog}">
             <local:PublicPassphrasePromptView/>

Paymetheus/CreateOrImportSeedView.xaml

@@ -0,0 +1,43 @@
+<UserControl x:Class="Paymetheus.CreateOrImportSeedView"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
+             xmlns:local="clr-namespace:Paymetheus"
+             mc:Ignorable="d" 
+             d:DesignHeight="300" d:DesignWidth="600">
+    <DockPanel Focusable="False">
+        <StackPanel DockPanel.Dock="Bottom" Orientation="Horizontal" HorizontalAlignment="Right">
+            <Button Content="Continue" IsDefault="True" Command="{Binding ContinueCommand}" Width="100" Margin="6,12,3,6" Padding="10 2"/>
+        </StackPanel>
+        <Label DockPanel.Dock="Top" FontSize="18" Content="Create or recover wallet"/>
+        <RadioButton GroupName="seedSelection" DockPanel.Dock="Top" Content="Create new wallet" IsChecked="{Binding CreateChecked}"/>
+        <RadioButton GroupName="seedSelection" DockPanel.Dock="Top" Content="Recover wallet from seed" IsChecked="{Binding ImportChecked}"/>
+        <Grid>
+            <StackPanel Visibility="{Binding CreateChecked, Converter={StaticResource hiddenConverter}}">
+                <Label>
+                    <TextBlock TextWrapping="Wrap">
+                        The wallet seed must be backed up before the wallet may be used.
+                        This seed is necessary to recover wallet keys in case of data loss.
+                        Write down this seed and save it in a secure location.
+                        The next prompt will require entering this seed to confirm it has been saved.
+                    </TextBlock>
+                </Label>
+                <Label Content="{Binding Bip0032SeedHex}" FontSize="16" HorizontalContentAlignment="Center"/>
+            </StackPanel>
+            <StackPanel Visibility="{Binding ImportChecked, Converter={StaticResource hiddenConverter}}">
+                <Label>
+                    <TextBlock TextWrapping="Wrap">
+                        The seed from a previously-created wallet may be used to recreate the wallet
+                        with all of its addresses and keys.  The seed should be formatted as a
+                        hexadecimal number (64 characters between 0-9 and A-F) or a list of
+                        mneumonic words.
+                    </TextBlock>
+                </Label>
+                <Label Content="Seed:"/>
+                <TextBox Text="{Binding ImportedSeed, Mode=OneWayToSource}"
+                         local:BindingProperties.UpdateSourceOnEnterProperty="TextBox.Text"/>
+            </StackPanel>
+        </Grid>
+    </DockPanel>
+</UserControl>

Paymetheus/DisplaySeedView.xaml.cs → Paymetheus/CreateOrImportSeedView.xaml.cs

@@ -1,7 +1,4 @@
-// Copyright (c) 2016 The btcsuite developers
-// Licensed under the ISC license.  See LICENSE file in the project root for full license information.
-
-using System;
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
@@ -19,11 +16,11 @@
 namespace Paymetheus
 {
     /// <summary>
-    /// Interaction logic for DisplaySeedView.xaml
+    /// Interaction logic for CreateOrImportSeedView.xaml
     /// </summary>
-    public partial class DisplaySeedView : UserControl
+    public partial class CreateOrImportSeedView : UserControl
     {
-        public DisplaySeedView()
+        public CreateOrImportSeedView()
         {
             InitializeComponent();
         }

Paymetheus/PassphraseDialogViewModel.cs

@@ -36,7 +36,7 @@ private async void ExecuteAction()
             }
             catch (Exception ex)
             {
-                MessageBox.Show(ex.Message);
+                MessageBox.Show(ex.ToString());
             }
         }
     }

Paymetheus/Paymetheus.csproj

@@ -138,9 +138,13 @@
       <DependentUpon>AccountView.xaml</DependentUpon>
     </Compile>
     <Compile Include="AccountViewModel.cs" />
+    <Compile Include="BindingProperties.cs" />
     <Compile Include="ConfirmSeedView.xaml.cs">
       <DependentUpon>ConfirmSeedView.xaml</DependentUpon>
     </Compile>
+    <Compile Include="CreateOrImportSeedView.xaml.cs">
+      <DependentUpon>CreateOrImportSeedView.xaml</DependentUpon>
+    </Compile>
     <Compile Include="StartupWizard.cs" />
     <Compile Include="ConnectionWizardView.xaml.cs">
       <DependentUpon>ConnectionWizardView.xaml</DependentUpon>
@@ -160,9 +164,6 @@
       <DependentUpon>CreateTransactionView.xaml</DependentUpon>
     </Compile>
     <Compile Include="DialogViewModelBase.cs" />
-    <Compile Include="DisplaySeedView.xaml.cs">
-      <DependentUpon>DisplaySeedView.xaml</DependentUpon>
-    </Compile>
     <Compile Include="ImportDialogView.xaml.cs">
       <DependentUpon>ImportDialogView.xaml</DependentUpon>
     </Compile>
@@ -232,11 +233,11 @@
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
     </Page>
-    <Page Include="CreateTransactionView.xaml">
+    <Page Include="CreateOrImportSeedView.xaml">
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
     </Page>
-    <Page Include="DisplaySeedView.xaml">
+    <Page Include="CreateTransactionView.xaml">
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
     </Page>