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Kickoff

After speaking with the OTRv4 team in regards to ChatSecure, there are some recommendations and things to follow for implementing OTRv4 there.

Ideas

Deciding between Swift and Objective-C

As it can be seen in the code from the OTR Kit on ChatSecure, the library is a wrapper of the C code, and it is written on Objective C.

Due to this, it uses wrappers to make the calls to the library itself and to the very different dependencies. For OTRv4, we will need to create other scripts (for libgoldilocks and libsodium), or use Objective C versions of them.

Notice that for libsodium:

For libgcrypt:

We can try using the same script, or use this library.

In order to implement it on ChatSecure, we, therefore, need to:

  • Decide between Swift and Objective C: while the first is the mostly recommeded, some C headers might not work with it. This has to be tested.
  • Write wrappers from the C code to either Swift or Objective C. This tutorial gives the basic insight for it. This might be interesting to follow as well.

Analyse the build scripts for the OTR kit

As it was noted, there are some build scripts for the dependencies of OTR. There can be found here. They should work the same.

Create an API

Basically, the way it used to work is as follows (there should be a main file, like this:

@protocol OTRKitDelegate <NSObject>
@required
/**
 *  This method **MUST** be implemented or OTR will not work. All outgoing messages
 *  should be sent first through OTRKit encodeMessage and then passed from this delegate
 *  to the appropriate chat protocol manager to send the actual message.
 *
 *  @param otrKit      reference to shared instance
 *  @param message     message to be sent over the network. may contain ciphertext.
 *  @param recipient   intended recipient of the message
 *  @param accountName your local account name
 *  @param protocol    protocol for account name such as "xmpp"
 *  @param tag optional tag to attached to message. Only used locally.
 */
- (void) otrKit:(OTRKit*)otrKit
  injectMessage:(NSString*)message
       username:(NSString*)username
    accountName:(NSString*)accountName
       protocol:(NSString*)protocol
            tag:(id)tag;

/**
 *  All outgoing messages should be sent to the OTRKit encodeMessage method before being
 *  sent over the network.
 *
 *  @param otrKit      reference to shared instance
 *  @param message     plaintext message
 *  @param sender      buddy who sent the message
 *  @param accountName your local account name
 *  @param protocol    protocol for account name such as "xmpp"
 *  @param tag optional tag to attach additional application-specific data to message. Only used locally.
 */
- (void) otrKit:(OTRKit*)otrKit
 encodedMessage:(NSString*)encodedMessage
       username:(NSString*)username
    accountName:(NSString*)accountName
       protocol:(NSString*)protocol
            tag:(id)tag
          error:(NSError*)error;


/**
 *  All incoming messages should be sent to the OTRKit decodeMessage method before being
 *  processed by your application. You should only display the messages coming from this delegate method.
 *
 *  @param otrKit      reference to shared instance
 *  @param message     plaintext message
 *  @param tlvs        OTRTLV values that may be present.
 *  @param sender      buddy who sent the message
 *  @param accountName your local account name
 *  @param protocol    protocol for account name such as "xmpp"
 *  @param tag optional tag to attach additional application-specific data to message. Only used locally.
 */
- (void) otrKit:(OTRKit*)otrKit
 decodedMessage:(NSString*)decodedMessage
           tlvs:(NSArray*)tlvs
       username:(NSString*)username
    accountName:(NSString*)accountName
       protocol:(NSString*)protocol
            tag:(id)tag;

/**
 *  When the encryption status changes this method is called
 *
 *  @param otrKit      reference to shared instance
 *  @param messageState plaintext, encrypted or finished
 *  @param username     buddy whose state has changed
 *  @param accountName your local account name
 *  @param protocol    protocol for account name such as "xmpp"
 */
- (void)    otrKit:(OTRKit*)otrKit
updateMessageState:(OTRKitMessageState)messageState
          username:(NSString*)username
       accountName:(NSString*)accountName
          protocol:(NSString*)protocol;
...

To encode a message:

/**
 * Encodes a message and optional array of OTRTLVs, splits it into fragments,
 * then injects the encoded data via the injectMessage: delegate method.
 * @param message The message to be encoded
 * @param tlvs Array of OTRTLVs, the data length of each TLV must be smaller than UINT16_MAX or it will be ignored.
 * @param recipient The intended recipient of the message
 * @param accountName Your account name
 * @param protocol the protocol of accountName, such as @"xmpp"
 *  @param tag optional tag to attach additional application-specific data to message. Only used locally.
 */
- (void)encodeMessage:(NSString*)message
                 tlvs:(NSArray*)tlvs
             username:(NSString*)username
          accountName:(NSString*)accountName
             protocol:(NSString*)protocol
                  tag:(id)tag;

To decode a message:

/**
 *  All messages should be sent through here before being processed by your program.
 *
 *  @param message     Encoded or plaintext incoming message
 *  @param sender      account name of buddy who sent the message
 *  @param accountName your account name
 *  @param protocol    the protocol of accountName, such as @"xmpp"
 *  @param tag optional tag to attach additional application-specific data to message. Only used locally.
 */
- (void)decodeMessage:(NSString*)message
             username:(NSString*)username
          accountName:(NSString*)accountName
             protocol:(NSString*)protocol
                  tag:(id)tag;