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https://github.com/marcoplaitano/c-cipher
A program to encrypt/decrypt files using the AES-CTR-256 cipher.
https://github.com/marcoplaitano/c-cipher
aes aes-256 aes-256-ctr aes-ctr aes-encryption c cipher cipher-algorithms encryption encryption-algorithms encryption-decryption password-manager
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A program to encrypt/decrypt files using the AES-CTR-256 cipher.
- Host: GitHub
- URL: https://github.com/marcoplaitano/c-cipher
- Owner: marcoplaitano
- License: mit
- Created: 2022-05-23T20:54:04.000Z (over 2 years ago)
- Default Branch: main
- Last Pushed: 2024-01-04T12:50:35.000Z (10 months ago)
- Last Synced: 2024-01-04T13:46:07.079Z (10 months ago)
- Topics: aes, aes-256, aes-256-ctr, aes-ctr, aes-encryption, c, cipher, cipher-algorithms, encryption, encryption-algorithms, encryption-decryption, password-manager
- Language: C
- Homepage:
- Size: 33.2 KB
- Stars: 0
- Watchers: 1
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# C-CIPHER
A program to encrypt/decrypt a file using the **AES-CTR-256** cipher.
It can be used to store passwords (or any other kind of sensible information)
locally, in a private way.
The user only needs one password to both encrypt and decrypt the information.
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## Details on Security
The algorithm is implemented in C, using the [OpenSSL]'s Encryption [API].
The **Encryption Key** has to be 256-bits long; it is generated by computing
`SHA256(p)`, with `p` being the user's password.[1](#f1)
The same key is used for both encryption and decryption.
The _Initialization Vector IV_ is a string of `16` bytes.
The last (**LSB**)[2](#f2) `8` bytes contain a counter which will be
incremented at every new encrypted block.
The first (**MSB**) `8` bytes contain the "_nonce_": a random sequence of bits.
When encrypting, the _nonce_ is filled with random bytes; these will be
prepended to the ciphertext in order to read them during the decryption
procedure.
The _block length n_, is an important parameter for determining the concrete
security of the cipher.
Being the **IV** a uniform string of _n-bits_, it is expected to repeat after
having performed "only" `2``n/2` encryptions.[3](#f3)
In our case `n` is `128` bits; this means that only `2``64` blocks -
or `2*10``5` **Petabytes** - can be safely encrypted without ever
changing the `IV`.
This is more than safe for a regular text file.
### Tampering
It must be noted that this mode of encryption provides no security against data
tampering.
If the ciphertext were to be modified even by just one bit, the *integrity* of
the information would be lost.
The scope of this project however is to provide a trivial example of encryption,
to be used for simpler "protection" against *adversaries* who know little to
nothing about cryptography.
**1** The usage of a **PBKDF** (Password-Based Key
Derivation Function) would further improve security.
**2** In **big-endian** order.
**3** Similar concept to '[The Birthday Problem]'.
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## Installation
Take a look at the [dependencies] listed below.
To download and compile the program:
```sh
git clone https://github.com/marcoplaitano/c-cipher
cd c-cipher
make
```
The executable file is `ccipher`.
To install it globally:
```sh
sudo make install
```
This will simply copy the executable to `/usr/local/bin/` and the manpage to
`usr/local/man/`.
Uninstall with:
```sh
sudo make uninstall
```
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## Usage
```sh
ccipher in-file out-file mode password
```
The program needs the following 4 command line arguments, in order:
+ `in-file`
Input file on which the cipher will be applied
+ `out-file`
Output file storing the result
+ `mode`
A string: either **encrypt**, **e**, **decrypt** or **d**
+ `password`
A string chosen by the user
_**Note:** using this approach means that anyone with access to the computer
can learn the password since it is stored in the shell's history.
A workaround might be requesting the 4 arguments **inside** the program, at
runtime._
### Example
The first time you run the program, the `in-file` should be the plain text file
containing the private information.
The output file will store the encrypted version of it.
It is at this point that you must choose the **password** to use. It can contain
any ASCII character and can be of any (reasonable) length.
```sh
ccipher input.txt private.dat e Password123
```
The following times, the plaintext version can be recreated with the command:
```sh
ccipher private.dat output.txt d Password123
```
Notice how the two paths have been swapped, the mode is now **d**ecrypt and the
password remains the same.
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## Dependencies
+ gcc
+ make
+ libssl3
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## Author
Marco Plaitano
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## License
Distributed under the [MIT] license.
[OpenSSL]:
https://www.openssl.org/
"Main Website"
[API]:
https://www.openssl.org/docs/man3.0/man3/EVP_aes_256_ctr.html
"Online Documentation"
[The Birthday Problem]:
https://en.wikipedia.org/wiki/Birthday_problem
"Wikipedia Article"
[dependencies]:
#dependencies
"Anchor to header"
[MIT]:
LICENSE
"Repository file"