OLMKit: New pickle version using a pickle key provided externally

Improve ObjC wrappers so that they can use a pickle key provided by the olm lib user.

This new behavior is optional to not break existing usage.

It is retro compatible and use pickle versioning already in place. 
Existing key will be unpickled with pickle v1 and pickled with pickle v2 if an external pickle key is provided.

xcode/OLMKit/OLMAccount.m

@@ -21,6 +21,7 @@
 #import "OLMSession.h"
 #import "OLMSession_Private.h"
 #import "OLMUtility.h"
+#import "OLMKit.h"
 
 @import Security;
 
@@ -243,6 +244,13 @@
 
         self = [self initWithSerializedData:pickle key:key error:&error];
     }
+    else if ([version isEqualToString:@"2"]) {
+        NSString *pickle = [decoder decodeObjectOfClass:[NSString class] forKey:@"pickle"];
+        NSData *key = OLMKit.sharedInstance.pickleKeyDelegate.pickleKey;
+        NSParameterAssert(key);
+        
+        self = [self initWithSerializedData:pickle key:key error:&error];
+    }
     
     NSParameterAssert(error == nil);
     NSParameterAssert(self != nil);
@@ -254,14 +262,23 @@
 }
 
 - (void)encodeWithCoder:(NSCoder *)encoder {
-    NSData *key = [OLMUtility randomBytesOfLength:32];
+    NSData *key = OLMKit.sharedInstance.pickleKeyDelegate.pickleKey;
+    if (key)
+    {
+        [encoder encodeObject:@"2" forKey:@"version"];
+    }
+    else
+    {
+        key = [OLMUtility randomBytesOfLength:32];
+        [encoder encodeObject:key forKey:@"key"];
+        [encoder encodeObject:@"1" forKey:@"version"];
+    }
+    
     NSError *error = nil;
     NSString *pickle = [self serializeDataWithKey:key error:&error];
     NSParameterAssert(pickle.length > 0 && error == nil);
     
     [encoder encodeObject:pickle forKey:@"pickle"];
-    [encoder encodeObject:key forKey:@"key"];
-    [encoder encodeObject:@"1" forKey:@"version"];
 }
 
 

xcode/OLMKit/OLMInboundGroupSession.m

@@ -19,6 +19,7 @@
 
 #import "OLMUtility.h"
 #include "olm/olm.h"
+#import "OLMKit.h"
 
 @interface OLMInboundGroupSession ()
 {
@@ -277,6 +278,13 @@
 
         self = [self initWithSerializedData:pickle key:key error:&error];
     }
+    else if ([version isEqualToString:@"2"]) {
+        NSString *pickle = [decoder decodeObjectOfClass:[NSString class] forKey:@"pickle"];
+        NSData *key = OLMKit.sharedInstance.pickleKeyDelegate.pickleKey;
+        NSParameterAssert(key);
+        
+        self = [self initWithSerializedData:pickle key:key error:&error];
+    }
     
     NSParameterAssert(error == nil);
     NSParameterAssert(self != nil);
@@ -288,14 +296,23 @@
 }
 
 - (void)encodeWithCoder:(NSCoder *)encoder {
-    NSData *key = [OLMUtility randomBytesOfLength:32];
+    NSData *key = OLMKit.sharedInstance.pickleKeyDelegate.pickleKey;
+    if (key)
+    {
+        [encoder encodeObject:@"2" forKey:@"version"];
+    }
+    else
+    {
+        key = [OLMUtility randomBytesOfLength:32];
+        [encoder encodeObject:key forKey:@"key"];
+        [encoder encodeObject:@"1" forKey:@"version"];
+    }
+    
     NSError *error = nil;
     NSString *pickle = [self serializeDataWithKey:key error:&error];
     NSParameterAssert(pickle.length > 0 && error == nil);
     
     [encoder encodeObject:pickle forKey:@"pickle"];
-    [encoder encodeObject:key forKey:@"key"];
-    [encoder encodeObject:@"1" forKey:@"version"];
 }
 
 @end

xcode/OLMKit/OLMKit.h

@@ -31,9 +31,31 @@
 #import <OLMKit/OLMPkSigning.h>
 #import <OLMKit/OLMSAS.h>
 
-@interface OLMKit : NSObject
 
-//! Project version string for OLMKit, the same as libolm.
-+ (NSString*)versionString;
+NS_ASSUME_NONNULL_BEGIN
+
+/**
+ `OLMKitPickleKeyDelegate` provides the key to use for every pickle operation.
+ */
+@protocol OLMKitPickleKeyDelegate <NSObject>
+
+- (NSData*)pickleKey;
 
 @end
+
+
+@interface OLMKit : NSObject
+
+/// Project version string for OLMKit, the same as libolm.
++ (NSString*)versionString;
+
+/// The optional delegate that provides the pickle key.
+/// If not provided, OLMKit will use default pickle keys.
+@property (nonatomic, weak, nullable) id<OLMKitPickleKeyDelegate> pickleKeyDelegate;
+
+/// The singleton instance.
++ (instancetype)sharedInstance;
+
+@end
+
+NS_ASSUME_NONNULL_END

xcode/OLMKit/OLMKit.m

@@ -30,4 +30,15 @@
     return [NSString stringWithFormat:@"%tu.%tu.%tu", major, minor, patch];
 }
 
++ (instancetype)sharedInstance
+{
+    static OLMKit *sharedInstance = nil;
+    
+    static dispatch_once_t onceToken;
+    dispatch_once(&onceToken, ^{
+        sharedInstance = [[self alloc] init];
+    });
+    return sharedInstance;
+}
+
 @end

xcode/OLMKit/OLMOutboundGroupSession.m

@@ -20,6 +20,8 @@
 #import "OLMUtility.h"
 #include "olm/olm.h"
 
+#import "OLMKit.h"
+
 @interface OLMOutboundGroupSession ()
 {
     OlmOutboundGroupSession *session;
@@ -198,6 +200,14 @@
 
         self = [self initWithSerializedData:pickle key:key error:&error];
     }
+    else if ([version isEqualToString:@"2"]) {
+        NSString *pickle = [decoder decodeObjectOfClass:[NSString class] forKey:@"pickle"];
+        NSData *key = OLMKit.sharedInstance.pickleKeyDelegate.pickleKey;
+        NSParameterAssert(key);
+        
+        self = [self initWithSerializedData:pickle key:key error:&error];
+    }
+        
 
     NSParameterAssert(error == nil);
     NSParameterAssert(self != nil);
@@ -209,14 +219,23 @@
 }
 
 - (void)encodeWithCoder:(NSCoder *)encoder {
-    NSData *key = [OLMUtility randomBytesOfLength:32];
+    NSData *key = OLMKit.sharedInstance.pickleKeyDelegate.pickleKey;
+    if (key)
+    {
+        [encoder encodeObject:@"2" forKey:@"version"];
+    }
+    else
+    {
+        key = [OLMUtility randomBytesOfLength:32];
+        [encoder encodeObject:key forKey:@"key"];
+        [encoder encodeObject:@"1" forKey:@"version"];
+    }
+
     NSError *error = nil;
     NSString *pickle = [self serializeDataWithKey:key error:&error];
     NSParameterAssert(pickle.length > 0 && error == nil);
 
     [encoder encodeObject:pickle forKey:@"pickle"];
-    [encoder encodeObject:key forKey:@"key"];
-    [encoder encodeObject:@"1" forKey:@"version"];
 }
 
 @end

xcode/OLMKit/OLMPkDecryption.m

@@ -19,6 +19,7 @@
 #include "olm/olm.h"
 #include "olm/pk.h"
 #include "OLMUtility.h"
+#import "OLMKit.h"
 
 @interface OLMPkDecryption ()
 {
@@ -274,6 +275,13 @@
 
         self = [self initWithSerializedData:pickle key:key error:&error];
     }
+    else if ([version isEqualToString:@"2"]) {
+        NSString *pickle = [decoder decodeObjectOfClass:[NSString class] forKey:@"pickle"];
+        NSData *key = OLMKit.sharedInstance.pickleKeyDelegate.pickleKey;
+        NSParameterAssert(key);
+        
+        self = [self initWithSerializedData:pickle key:key error:&error];
+    }
     
     NSParameterAssert(error == nil);
     NSParameterAssert(self != nil);
@@ -285,15 +293,23 @@
 }
 
 - (void)encodeWithCoder:(NSCoder *)encoder {
-    NSData *key = [OLMUtility randomBytesOfLength:32];
-    NSError *error = nil;
-    
-    NSString *pickle = [self serializeDataWithKey:key error:&error];
-    NSParameterAssert(pickle.length > 0 && error == nil);
-
-    [encoder encodeObject:pickle forKey:@"pickle"];
+    NSData *key = OLMKit.sharedInstance.pickleKeyDelegate.pickleKey;
+    if (key)
+    {
+        [encoder encodeObject:@"2" forKey:@"version"];
+    }
+    else
+    {
+        key = [OLMUtility randomBytesOfLength:32];
         [encoder encodeObject:key forKey:@"key"];
         [encoder encodeObject:@"1" forKey:@"version"];
     }
     
+    NSError *error = nil;
+    NSString *pickle = [self serializeDataWithKey:key error:&error];
+    NSParameterAssert(pickle.length > 0 && error == nil);
+    
+    [encoder encodeObject:pickle forKey:@"pickle"];
+}
+
 @end