225 lines
11 KiB
Markdown
225 lines
11 KiB
Markdown
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Introduction
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============
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SlunkCrypt is an experimental cryptography library and command-line tool.
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Legal Warning
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=============
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Use of SlunkCrypt may be illegal in countries where encryption is outlawed. We believe it is legal to use SlunkCrypt in many countries all around the world, but we are not lawyers, and so if in doubt you should seek legal advice before downloading it. You may find useful information at [cryptolaw.org](http://www.cryptolaw.org/), which collects information on cryptography laws in many countries, but we can't vouch for its correctness.
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Command-line Usage
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==================
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This section describes the SlunkCypt command-line application.
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Synopsis
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--------
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The SlunkCypt command-line program is invoked as follows:
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slunkcrypt --encrypt [[@][:]<passphrase>] <input> <output>
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slunkcrypt --decrypt [[@][:]<passphrase>] <input> <output>
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slunkcrypt --make-pw [<length>]
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Commands
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--------
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One of the following commands must be chosen:
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- **`--encrypt` (`-e`):**
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Run application in ***encrypt*** mode. Reads the given *plaintext* and generates *ciphertext*.
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- **`--decrypt` (`-d`):**
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Run application in ***decrypt*** mode. Reads the given *ciphertext* and restores *plaintext*.
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- **`--make-pw` (`-p`):**
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Generate and output a "strong" random passphrase suitable for use with SlunkCrypt.
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- **`--self-test` (`-t`):**
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Run application in ***self-test*** mode. Program will exit when test is completed.
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Options
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-------
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The following options are available:
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- **`<passphrase>`**:
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* The passphrase used to "protect" the message. The same passphrase must be used for both, ***encrypt*** and ***decrypt*** mode.
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* It will only be possible decrypt the ciphertext, if the "correct" passphrase is known.
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* Use **`--make-pw`** to generate a random passphrase. The passphrase must be kept confidential under all circumstances!
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* **Syntax:**
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- If the passphrase is prefixed with an **`@`** character, then it specifies the file to read the passphrase from.
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- If the passphrase is set to **`@-`**, then the passphrase is read from the standard input stream.
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- If the passphrase is prefixed with an **`:`** character, then the leading character is ignored; use if passphrase contains **`@`** character.
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- If the parameter is *omitted*, then the passphrase is read from the `SLUNK_PASSPHRASE` environment variable.
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* *Note:* In order to thwart brute force attacks, it is recommended to choose a "random" password that is at least 12 characters in length and that consists of upper-case characters, lower-case characters, digits as well as other "special" characters.
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- **`<input>`**:
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* In ***encrypt*** mode, specifies the *plaintext* (unencrypted information) file that is to be encrypted.
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* In ***decrypt*** mode, specifies the *ciphertext* (result of encryption) file that is to be decrypted.
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- **`<output>`**:
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* In ***encrypt*** mode, specifies the file where the *ciphertext* (result of encryption) will be stored.
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* In ***decrypt*** mode, specifies the file where the *plaintext* (unencrypted information) will be stored.
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- **`<length>`**:
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* Speicifes the length of the passphrase to be generated, in characters. If *not* specified, defaults to 24.
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Programming Interface (API)
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===========================
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C99 API
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-------
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This section describes the "low-level" C99 API of the SlunkCypt library.
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### slunkcrypt_alloc()
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Allocate and initialize a new SlunkCrypt encryption/decryption context.
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slunkcrypt_t slunkcrypt_alloc(
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const uint64_t nonce,
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const uint8_t *const passwd,
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const size_t passwd_len
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);
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***Parameters:***
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* `nonce`
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The *nonce* (number used once) to be used for the encryption/decryption process. The purpose of the nonce is to ensure that each message will be encrypted differently, even when the same password is used to encrypt *multiple* (possibly identical) messages. Therefore, a new *random* nonce **must** be chosen for each message to be encrypted! It is *not* necessary to keep the nonce confidential, but the same nonce **must** be used for both, encryption *and* decryption. Typically, the nonce is stored/transmitted alongside the ciphertext.
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*Note:* It is recommended to generate a random nonce via the `slunkcrypt_generate_nonce()` function for each message!
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* `passwd`
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The password to "protect" the message. The password is given as an array of bytes (`uint8_t`), e.g. UTF-8 encoded characters; a terminating NULL character is *not* required, as the length of the password is specified explicitly. The same password **may** be used to encrypt *multiple* messages. Also, the same password **must** be used for both, encryption *and* decryption; it will *only* be possible decrypt the ciphertext, if the "correct" password is known. The password must be kept confidential under all circumstances!
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*Note:* In order to thwart *brute force* attacks, it is recommended to choose a "random" password that is at least 12 characters in length and that consists of upper-case characters, lower-case characters, digits as well as other "special" characters.
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* `passwd_len`
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The length of password given by the `passwd` parameter, in bytes, **not** counting a terminating NULL character. The minimum/maximum length of the password are given by the `SLUNKCRYPT_PWDLEN_MIN` and `SLUNKCRYPT_PWDLEN_MAX` constants, respectively.
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***Return value:***
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* If successful, a handle to the new SlunkCrypt context is return; otherwise `SLUNKCRYPT_NULL` is returned.
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*Note:* Applications **should** treat `slunkcrypt_t` as an *opaque* handle type. Also, as soon as the SlunkCrypt context is *not* needed anymore, the application **shall** call `slunkcrypt_free()` in order to "clear" and de-allocate that context.
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### slunkcrypt_reset()
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Re-initialize an existing SlunkCrypt encryption/decryption context.
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int slunkcrypt_reset(
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const slunkcrypt_t context,
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const uint64_t nonce,
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const uint8_t *const passwd,
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const size_t passwd_len
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);
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***Parameters:***
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* `context`
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The existing SlunkCrypt context to be re-initialized. This must be a valid handle that was returned by a previous invocation of the `slunkcrypt_alloc()` function and that has **not** been `free`'d since then.
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* `nonce`
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Please refer to the `slunkcrypt_alloc()` function for details!
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* `passwd`
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Please refer to the `slunkcrypt_alloc()` function for details!
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* `passwd_len`
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Please refer to the `slunkcrypt_alloc()` function for details!
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***Return value:***
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* If successful, `SLUNKCRYPT_SUCCESS` is returned; otherwise `SLUNKCRYPT_FAILURE` or `SLUNKCRYPT_ABORTED` is returned.
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### slunkcrypt_free()
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De-allocate an existing SlunkCrypt encryption/decryption context. This will "clear" and release any memory occupied by the context.
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void slunkcrypt_free(
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const slunkcrypt_t context
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);
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***Parameters:***
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* `context`
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The existing SlunkCrypt context to be de-allocated. This must be a valid handle that was returned by a previous invocation of the `slunkcrypt_alloc()` function and that has **not** been `free`'d since then.
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*Note:* Once a handle has been passed to this function, that handle is *invalidated* and **must not** be used again!
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### slunkcrypt_generate_nonce()
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Generate a new random *nonce* (number used once), using the system's "cryptographically secure" entropy source.
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int slunkcrypt_generate_nonce(
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int64_t* const nonce
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);
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***Parameters:***
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* `nonce`
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A pointer to a variable of type `int64_t` that receives the new random nonce.
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***Return value:***
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* If successful, `SLUNKCRYPT_SUCCESS` is returned; otherwise `SLUNKCRYPT_FAILURE` or `SLUNKCRYPT_ABORTED` is returned.
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### slunkcrypt_encrypt()
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Encrypt the next message chunk, using separate input/output buffers.
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int slunkcrypt_encrypt(
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const slunkcrypt_t context,
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const uint8_t *const input,
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uint8_t* const output,
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size_t length
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);
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***Parameters:***
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* `context`
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The existing SlunkCrypt context to be used for encrypting the message chunk. This context will be updated.
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* `input`
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A pointer to the *input* buffer containing the next chunk of the plaintext to be encrypted. The plaintext is given as an array of bytes (`uint8_t`). This can be arbitrary binary data, e.g. UTF-8 encoded text. NULL bytes are **not** treated specially.
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The *input* buffer must contain *at least* `length` bytes of data. If the buffer is longer than `length` bytes, then only the first `length` bytes will be processed and the remainder is ignored!
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* `output`
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A pointer to the *output* buffer where the ciphertext chunk that corresponds to the given plaintext chunk will be stored. The ciphertext is stored as an array of bytes (`uint8_t`); it has the same length as the plaintext data.
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The *output* buffer must provide sufficient space for storing *at least* `length` bytes of encrypted data. If the buffer is longer than `length` bytes, then only the first `length` bytes of the buffer will be filled with encrypted data!
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* `length`
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The length of the plaintext chunk contained in the *input* buffer given by the `input` parameter, in bytes. At the same time, this determines the minimum required size of the *output* buffer given by the `output` parameters, in bytes.
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***Return value:***
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* If successful, `SLUNKCRYPT_SUCCESS` is returned; otherwise `SLUNKCRYPT_FAILURE` or `SLUNKCRYPT_ABORTED` is returned.
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### slunkcrypt_encrypt_inplace()
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Encrypt the next message chunk, using a single buffer.
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int slunkcrypt_encrypt(
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const slunkcrypt_t context,
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uint8_t* const buffer,
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size_t length
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);
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***Parameters:***
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* `context`
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The existing SlunkCrypt context to be used for encrypting the message chunk. This context will be updated.
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* `buffer`
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A pointer to the buffer initially containing the next chunk of the plaintext to be encrypted. The plaintext is given as an array of bytes (`uint8_t`). This can be arbitrary binary data, e.g. UTF-8 encoded text. NULL bytes are **not** treated specially. The ciphertext chunk that corresponds to the given plaintext chunk will be stored to the *same* buffer, thus replacing the plaintext data.
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The buffer must initially contain *at least* `length` bytes of input data; the first `length` bytes of the buffer will be overwritten with the encrypted data. If the buffer is longer than `length` bytes, then only the first `length` bytes will be processed and overwritten.
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* `length`
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The length of the plaintext chunk initially contained in the input/output buffer given by the `buffer` parameter, in bytes. At the same time, this determines the portion of the input/output buffer that will be overwritten with encrypted data, in bytes.
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***Return value:***
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* If successful, `SLUNKCRYPT_SUCCESS` is returned; otherwise `SLUNKCRYPT_FAILURE` or `SLUNKCRYPT_ABORTED` is returned.
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License
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=======
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This work has been released under the **CC0 1.0 Universal** license.
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For details, please refer to:
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<https://creativecommons.org/publicdomain/zero/1.0/legalcode>
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