|Initial release||October 12, 2011|
|Operating system||iOS, OS X|
|Type||Instant messaging service|
iMessage was announced by Scott Forstall at the WWDC 2011 keynote on June 6, 2011. A version of the iOS Messages application with support for iMessage was included in the iOS 5 update on October 12, 2011.
On February 16, 2012, Apple announced that a new OS X Messages application with support for iMessage, replacing iChat, would be part of OS X Mountain Lion. Mountain Lion, with Messages, was released on July 25, 2012.
On October 23, 2012, Apple CEO, Tim Cook announced that Apple device users have sent 300 billion messages using iMessage and that Apple delivers an average of 28,000 messages per second.
On November 4, 2014, iMessage scored 5 out of 7 points on the Electronic Frontier Foundation's secure messaging scorecard. It lost points because users can't verify contacts' identities and because the code is not open to independent review.
On November 12, 2012, Chetan Sharma, a technology and strategy consulting firm, published the US Mobile Data Market Update Q3 2012, noting the decline of text messaging in the United States, and suggested the decline may be attributed to Americans using alternative free messaging services such as iMessage.
iMessage allows users to send texts, documents, photos, videos, contact information, and group messages over Wi-Fi, mobile phone Internet access, or other forms of Internet access to other iOS or OS X users, thus providing an alternative to standard SMS/MMS messaging for most users with devices running iOS 5 or later.
iMessage is accessible through the Messages app on an iPhone, iPad or iPod touch running iOS 5 or later or on a Mac running OS X Mountain Lion or later. Owners of these devices can register one or more email addresses with Apple, and, additionally, iPhone owners can register their phone numbers with Apple, provided their carrier is supported. When a message is sent to a mobile number, Messages will check with Apple if the mobile number is set up for iMessage. If it is, then the message will seamlessly transition from SMS to iMessage.
In Messages, the user's sent communication is aligned to the right, with replies from other people on the left. A user can see if the other iMessage user is typing a message, pale gray ellipsis appears in the text bubble of the other user when a reply is started. It is also possible to start a conversation on one iOS device and continue it on another. iMessage-specific functions operate only between machines running iOS 5 or later or running Mountain Lion or later, but, on the iPhone, Messages can use SMS to communicate with non-iOS devices, or with other iPhones when iMessage is unavailable. On iPhones, green buttons and text bubbles indicate SMS-based communication; on all iOS devices, blue buttons and text bubbles indicate iMessage communication.
All iMessages are encrypted and can be tracked using delivery receipts. If the recipient enables Read Receipts, the sender will be able to see that the recipient has read the message.
iMessage also allows users to set up chats with more than two people - a "group chat". However, the group chatting features do not integrate very well with members in the group who have a different type of phone.
If the iPhone is running iOS 5 or greater, the messaging app will send text messages as an iMessage instead of the usual text message. This means that if you are sending text messages with another iOS 5 user, there is no SMS charge associated with the messaging. It is merely treated as an additional data transfer.
iMessage is very similar to MMS: it not only allows the user to send plain text, but also allows the user to send pictures, movies, locations, and contacts.
While there are sources that claim the iMessage protocol is based on XMPP, the protocol is actually based on the Apple Push Notification Service (APNs) – a proprietary, binary protocol. It sets up a Keep-Alive connection with the Apple servers. Every connection has its own unique code, which acts as an identifier for the route that should be used to send a message to a specific device. The connection is encrypted with TLS using a client side certificate, that is requested by the device on the activation of iMessage.
Apple claims that iMessages are protected by end-to-end encryption "so no one but the sender and receiver can access them" and assures that "[Apple] cannot decrypt the data" and "[Apple does] not log messages". Because iMessage does not display its users' fingerprints for off-band verification of received public keys, users are unable to verify there is not a man in the middle. Apple's co-operation is not mandatory, as transparent MITM can also be established by exploiting known weaknesses of public key infrastructure. For example, using a stolen private key of Apple server or private key of a Certificate authority that the client trusts, an attacker (e.g. a nation state) is able to pose as the Apple's directory service, and inject rogue public key(s).
Multiple news reporters have verified allegations that if a user switches from an Apple device to a non-Apple device, messages being delivered to them through iMessage will not reach their destination. A lawsuit has been filed against Apple over this issue. In November 2014 Apple addressed this problem by providing instructions and an online tool to deregister iMessage.
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