TigerMail - Alternatives

Dark Mail

How it works:

Decentralized net (with servers and users registered on them, just like regular email).
Mandatory encryption. Servers and users have their own keys.
Parts of message are encrypted with different keys. Envelope is for mail server, message contents for recipient.
User keys can be stored on sever or owned by users.
Email spoofing is not possible.

Advantages:

Disadvantages:

No forward secrecy.
Specification is incomplete and development is slow (it's one person's project right now).

How it works:

Distributed (p2p) network.
Users are identified by checksum of public key.
Messages are broadcasted (there is a smart algorithm that makes broadcasting more efficient than sending to everyone), only recipient can decrypt.
A small proof-of-work is added to prevent spamming.

Disadvantages:

How it works:

Disadvantages:

Some background about Freenet (see documentation):

Distributed (p2p) network.
Freenet is a distributed filesystem, where any user can upload a file, it's contents are encrypted and distributed in small chunks for storage among many other nodes.
There are multiple ways to refer to data:
- "Content Hash Key" (CHK) allows for immutable storage, where data is identified by checksum.
- Signed Subspace Key (SSK) allows for updateable storage, where data is identified by a public key and version number. Data is signed with corresponding private key. Under a single key multiple files can be stored as a directory tree.
- "Updateable Subspace Key" (USK) is the same as SSK, but client automatically tries to find latest version.
- "Keyword Signed Key" (KSK) allows to store unprotected data under an arbitrary name. Anyone can change it.
"Web of Trust" (WoT) is a subsystem, where users are identified by USK keys.

How Freemail works (see spec):

Alice and Bob create their mailboxes by publishing a mailsite file under their WoT keys. It contains a RSA-4096 public key and a random string named rtsksk.
When Alice wants to send her first message to Bob, she creates a "Request To Send" (RTS) message which allows to create communication channel. RTS contains:
- USK key pointing to Alice's mailsite.
- Bob's address.
- Randomly generated SSK private key for channel.
- Random values fetchslot and sendslot (description below).
- Expiration date.
Alice signs RTS with her mailsite key and encrypts with Bob's mailsite key.
Alice publishes RTS under KSK key created from Bob's rtksks value, date and a natural number (Alice iterates it until first unused KSK key is found).
Bob downloads and decrypts Alice's RTS message.
Alice and Bob now share a SSK private key used as communication channel.
Alice sends messages by storing them under filename i (like "initiator") and Bob under r (like "recipient"). As a first version number Alice uses fetchslot an Bob sendslot. Each next version number is derived from SHA-256 checksum of previous one.

Advantages:

Disadvantages:

No true forward secrecy.
Using KSK keys for storing RTS message allows for easy denial of service attack.

How it works (see techdoc):

Uses I2P anonymizing distributed (p2p) network.
Users are identified by public key.
Sending message:
- Encrypted with recipient key.
- Divided into 30kb chunks
- Each chunk stored in Kademlia DHT.
- DHT keys of all chunks are written into an "index" file.
- Index file is stored under DHT key equal to SHA-256 sum of recipient address (network allows to store multiple files under a signle key).
Message is stored for 100 days.
Each chunk of data contains a SHA-256 checksum of "delete authorization" packet. This packet is included in the message and encrypted with the receiver key. The receiver can use it to request deletion of data from DHT.

Advantages:

Disadvantages: