DeepCoder is available as a freeware version and as a registered version.
The freeware version has a reduced encryption strength (AES 56 bits). The registered version has the full encryption strength (AES 256 bits).

E-mail
One thing you must know is that when you send an e-mail to someone, that e-mail passes tens maybe hundreds of computers (mailservers). If somebody wants to, he can easily intercept your e-mail and read it.
You see, sending an e-mail is like sending someone a message on a postcard on traditional 'snail mail'... If you want to send a private message to someone through traditional (snail) mail, you don't send a postcard. I assume you write your message on a piece of paper, put that paper in an envelope and send the envelope. Even if the message is not at all that confidential..
You could say that DeepCoder provides you with an envelope to send your e-mail in. DeepCoder encrypts your message and makes it unreadable to anyone, except the person you send the mail to. Such a 'message' can be ordinary text, but it can also include one or more files.

Files
You probably have files stored on your computers harddisk with personal or confidential information.
If you are sure that nobody can get access to those files, then your privacy is not in danger.

If, on the other hand, you know that other people can easily get access to your computer and your files and you don't want them to read your files, DeepCoder is just the tool for you.
With DeepCoder you can encrypt your files so that nobody but you (or someone else who has the key) can read your files.

Digital signatures and message authentication
If you receive an e-mail from someone, how can you be sure that this mail really was sent by the person who is listed as the sender in that mail? It is extremely easy to send an e-mail and put someone elses name on it as the sender.
DeepCoder allows you to use digital signatures. The person who receives such a mail (or file) that was digitally signed, can check this signature. If the signature matches, he can be sure that this mail was really sent by the person who's signature is on the mail.
At the same time he can verify that this mail was not modified since it was signed. This is called Message Authentication.

You can compare a digital signature with a pen-and-paper signature. When you sign a piece of paper, the person in possession of that signed paper can be sure that you agree with the contents of the paper and that you have read its contents.
A digital signature pretty much serves the same purpose. The difference is that a digital signature is practically impossible to forge, compared with a pen-and-paper signature.

Self-extracting archives
With DeepCoder you can create archives (that can contain a textmessage and/or multiple files) that are 'self-extracting'.
This means that the archive is turned into a program. This allows you to send encrypted information (text and files) to someone who does not have DeepCoder installed. This person simply executes the self-extracting file you sent him, enters the secret password and he can read all the files and text you stored in the self-extracting archive.

• DeepCoder works with any POP3 e-mail client (like Outlook, Outlook Express, Eudora, Pegasus, ...) or a browser for webmail (Yahoo! mail, Hotmail, GMail, ...) to encrypt and decrypt e-mails.
• DeepCoder works with any wordprocessing program to encrypt and decrypt (parts of) text.
• DeepCoder can encrypt and decrypt files.
• DeepCoder can create encrypted and compressed archives with multiple files and an optional textmessage.
• DeepCoder uses secret key encryption and public key encryption.
• Digital signatures: DeepCoder can digitally sign your e-mails and files. You can even have files signed by multiple people.
• DeepCoder can create self-extracting archives so you can send encrypted files and/or textmessages to people who do not have DeepCoder installed.
• Encrypt and/or decrypt files by simple drag-and-drop.
• Encrypt and/or decrypt textmessages by pressing a hotkey (or many other ways...)

• Public (assymmetric) key encryption: RSA according to PKCS #1 V1.5. Keysize: 288 to 32768 bits.
• Secret (symmetric) key encryption: AES (Rijndael), 256 bits keysize in CBC mode. (56 bits in the freeware version).
• Hash algorithm: Secure Hash Algorithm SHA-256
• Message authentication: HMAC according to FIPS 198a and/or RFC 2104.
• Key Deriving Function (to turn a passphrase into a key): PKCS #5  PBKDF1.
• Digital signature: RSA according to PKCS #1 V1.5  with SHA-256 as hash function
• Pseudo Random Number Generator for session key generation: Blum-Blum-Shub.
• Compression algorithms: LZ78 and LZSS.

First of all, what is a key?
A key is a piece of information that you need to encrypt information. The person who wants to decrypt the encrypted data, will need the same key in order to decrypt the data.

Secret key encryption
With secret key (or symmetric key) encryption, you use a password, or better, a passphrase as a key to encrypt your data.
To decrypt the data, the other person needs the same passphrase. So both parties need the same key, that's why this is also called symmetric key encryption.
DeepCoder converts your passphrase into a 256 bits key. (or into a 56 bits key in the freeware version).

Public key encryption
With public key encryption you do not have to enter a passphrase, instead, you let DeepCoder calculate a public key for you. You see, a public key is nothing but a huge number, hundreds or thousands of digits long.
To be more specific, a public key consists of 2 numbers that form a pair, a keypair. One of the 2 numbers is called the private key, the other is called the public key.
Everybody who wants to send you an encrypted message, needs your public key to encrypt the message. To decrypt that message, you need your private key.
This implies two things: you need to distribute your public key to everyone of your contact persons. In fact, you can even put it on your website if you have one, so the whole world can find your public key.
Your private key however, since you need it to decrypt messages, must be kept secret at all times!

In DeepCoder, you can select a public key keylength between 288 and 32768 bits. Do not compare the secret key keylength of 256 bits with the public key keylengths! They are 2 different things. Comparing them is like comparing apples with oranges.
A 128 bits secret key is supposed to be as strong as a 3000 bit public key.