311 lines
12 KiB
Markdown
311 lines
12 KiB
Markdown
[](https://travis-ci.org/jedisct1/libsodium?branch=master)
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============
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[NaCl](http://nacl.cr.yp.to/) (pronounced "salt") is a new easy-to-use
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high-speed software library for network communication, encryption,
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decryption, signatures, etc.
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NaCl's goal is to provide all of the core operations needed to build
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higher-level cryptographic tools.
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Sodium is a portable, cross-compilable, installable, packageable
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fork of NaCl (based on the latest released upstream version [nacl-20110221](http://hyperelliptic.org/nacl/nacl-20110221.tar.bz2)), with a compatible API.
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The design choices, particularly in regard to the Curve25519
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Diffie-Hellman function, emphasize security (whereas NIST curves
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emphasize "performance" at the cost of security), and "magic
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constants" in NaCl/Sodium have clear rationales.
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The same cannot be said of NIST curves, where the specific origins of
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certain constants are not described by the standards.
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And despite the emphasis on higher security, primitives are faster
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across-the-board than most implementations of the NIST standards.
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## Portability
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In order to pick the fastest working implementation of each primitive,
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NaCl performs tests and benchmarks at compile-time. Unfortunately, the
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resulting library is not guaranteed to work on different hardware.
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Sodium performs tests at run-time, so that the same binary package can
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still run everywhere.
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Sodium is tested on a variety of compilers and operating systems,
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including Windows (with MingW or Visual Studio, x86 and x64), iOS and Android.
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## Installation
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Sodium is a shared library with a machine-independent set of
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headers, so that it can easily be used by 3rd party projects.
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The library is built using autotools, making it easy to package.
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Installation is trivial, and both compilation and testing can take
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advantage of multiple CPU cores.
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Download a
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[tarball of libsodium](https://download.libsodium.org/libsodium/releases/),
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then follow the ritual:
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./configure
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make && make check && make install
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Pre-compiled Win32 packages are available for download at the same
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location.
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Integrity of source tarballs can currently be checked using PGP or
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verified DNS queries (`dig +dnssec +short txt <file>.download.libsodium.org`
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returns the SHA256 of any file available for download).
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## Pre-built binaries
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Pre-built libraries for Visual studio 2010, 2012 and 2013, both for
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x86 and x64, are available for download at
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https://download.libsodium.org/libsodium/releases/ , courtesy of
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Samuel Neves (@sneves).
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## Comparison with vanilla NaCl
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Sodium does not ship C++ bindings. These might be part of a distinct
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package.
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The default public-key signature system in NaCl was a prototype that
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shouldn't be used any more.
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Sodium ships with the SUPERCOP reference implementation of
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[Ed25519](http://ed25519.cr.yp.to/), and uses this system by default
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for `crypto_sign*` operations.
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For backward compatibility, the previous system is still compiled in,
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as `crypto_sign_edwards25519sha512batch*`.
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## Additional features
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The Sodium library provides some convenience functions in order to retrieve
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the current version of the package and of the shared library:
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const char *sodium_version_string(void);
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const int sodium_library_version_major(void);
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const int sodium_library_version_minor(void);
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Headers are installed in `${prefix}/include/sodium`.
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A convenience header includes everything you need to use the library:
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#include <sodium.h>
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This is not required, however, before any other libsodium functions, it
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is recommended to call:
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sodium_init();
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This will pick optimized implementations of some primitives, if they
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appear to work as expected after running some tests, and these will be
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used for subsequent operations.
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It will also initialize the pseudorandom number generator.
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This function should only be called once, and before performing any other
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operations.
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Doing so is required to ensure thread safety of all the functions provided by
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the library.
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Sodium also provides helper functions to generate random numbers,
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leveraging `/dev/urandom` or `/dev/random` on *nix and the cryptographic
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service provider on Windows. The interface is similar to
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`arc4random(3)`. It is `fork(2)`-safe but not thread-safe. This holds
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true for `crypto_sign_keypair()` and `crypto_box_keypair()` as well.
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uint32_t randombytes_random(void);
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Return a random 32-bit unsigned value.
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void randombytes_stir(void);
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Generate a new key for the pseudorandom number generator. The file
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descriptor for the entropy source is kept open, so that the generator
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can be reseeded even in a chroot() jail.
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uint32_t randombytes_uniform(const uint32_t upper_bound);
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Return a value between 0 and upper_bound using a uniform distribution.
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void randombytes_buf(void * const buf, const size_t size);
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Fill the buffer `buf` with `size` random bytes.
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int randombytes_close(void);
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Close the file descriptor or the handle for the cryptographic service
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provider.
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A custom implementation of these functions can be registered with
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`randombytes_set_implementation()`.
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In addition, Sodium provides a function to securely wipe a memory
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region:
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void sodium_memzero(void * const pnt, const size_t size);
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Warning: if a region has been allocated on the heap, you still have
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to make sure that it can't get swapped to disk, possibly using
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`mlock(2)`.
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In order to compare memory zones in constant time, Sodium provides:
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int sodium_memcmp(const void * const b1_, const void * const b2_,
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size_t size);
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`sodium_memcmp()` returns `0` if `size` bytes at `b1_` and `b2_` are
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equal, another value if they are not. Unlike `memcmp()`,
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`sodium_memcmp()` cannot be used to put `b1_` and `b2_` into a defined
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order.
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And a convenience function for converting a binary buffer to a
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hexadecimal string:
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char * sodium_bin2hex(char * const hex, const size_t hexlen,
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const unsigned char *bin, const size_t binlen);
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## Easy interfaces to `crypto_box` and `crypto_secretbox`
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`crypto_box` and `crypto_secretbox` require prepending
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`crypto_box_ZEROBYTES` or `crypto_secretbox_ZEROBYTE` extra bytes to the
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message, and making sure that these are all zeros.
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A similar padding is required to decrypt the ciphertext. And this
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padding is actually larger than the MAC size,
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`crypto_box_MACBYTES`/`crypto_secretbox_MACBYTES`.
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This API, as defined by NaCl, can be confusing. And while using a
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larger buffer and two pointers is not an issue for native C
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applications, this might not be an option when another runtime is
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controlling the allocations.
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Libsodium provides an easy, higher-level interface to these operations.
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int crypto_box_easy(unsigned char *c, const unsigned char *m,
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unsigned long long mlen, const unsigned char *n,
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const unsigned char *pk, const unsigned char *sk);
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This function encrypts and authenticates a message `m` using the
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sender's secret key `sk`, the receiver's public key `pk` and a nonce
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`n`, which should be `crypto_box_NONCEBYTES` bytes long.
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The ciphertext, including the MAC, will be copied to `c`, whose length
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should be `len(m) + crypto_box_MACBYTES`, and that doesn't require to be
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initialized.
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int crypto_box_open_easy(unsigned char *m, const unsigned char *c,
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unsigned long long clen, const unsigned char *n,
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const unsigned char *pk, const unsigned char *sk);
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This function verifies and decrypts a ciphertext `c` as returned by
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`crypto_box_easy()`, whose length is `clen`, using the nonce `n`, the
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receiver's secret key `sk`, and the sender's public key `pk`. The
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message is stored to `m`, whose length should be at least `len(c) -
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crypto_box_MACBYTES` and that doesn't require to be initialized.
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Similarily, secret-key authenticated encryption provide "easy" wrappers:
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int crypto_secretbox_easy(unsigned char *c, const unsigned char *m,
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unsigned long long mlen, const unsigned char *n,
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const unsigned char *k);
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int crypto_secretbox_open_easy(unsigned char *m, const unsigned char *c,
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unsigned long long clen, const unsigned char *n,
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const unsigned char *k);
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The length of the ciphertext, which will include the MAC, is
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`len(m) + crypto_secretbox_MACBYTES`, and the length of the buffer for
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the decrypted message doesn't have to be more than `len(c) -
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crypto_secretbox_MACBYTES`.
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The "easy" interface currently requires allocations and copying, which
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makes it slower than using the traditional NaCl interface. This
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shouldn't make any sensible difference in most use cases, and future
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versions of the library may not require extra copy operations any
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more. Unless speed is absolutely critical, you are welcome to use the
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"easy" interface, especially if you are new to NaCl/Sodium.
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## New operations
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### crypto_shorthash
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A lot of applications and programming language implementations have
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been recently found to be vulnerable to denial-of-service attacks when
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a hash function with weak security guarantees, like Murmurhash 3, was
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used to construct a hash table.
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In order to address this, Sodium provides the “shorthash” function,
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currently implemented using SipHash-2-4. This very fast hash function
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outputs short, but unpredictable (without knowing the secret key)
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values suitable for picking a list in a hash table for a given key.
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See `crypto_shorthash.h` for details.
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### crypto_generichash
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This hash function provides:
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* A variable output length (up to `crypto_generichash_BYTES_MAX` bytes)
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* A variable key length (from no key at all to
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`crypto_generichash_KEYBYTES_MAX` bytes)
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* A simple interface as well as a streaming interface.
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`crypto_generichash` is currently being implemented using
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[Blake2](https://blake2.net/).
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## Constants available as functions
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In addition to constants for key sizes, output sizes and block sizes,
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Sodium provides these values through function calls, so that using
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them from different languages is easier.
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## Bindings for other languages
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* C++: [sodiumpp](https://github.com/rubendv/sodiumpp)
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* Erlang: [Erlang-NaCl](https://github.com/tonyg/erlang-nacl)
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* Erlang: [Salt](https://github.com/freza/salt)
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* Haskell: [Saltine](https://github.com/tel/saltine)
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* Idris: [Idris-Sodium](https://github.com/edwinb/sodium-idris)
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* Java: [Kalium](https://github.com/abstractj/kalium)
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* Java JNI: [Kalium-JNI](https://github.com/joshjdevl/kalium-jni)
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* Julia: [Sodium.jl](https://github.com/amitmurthy/Sodium.jl)
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* LUA: [lua-sodium](https://github.com/morfoh/lua-sodium)
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* .NET: [libsodium-net](https://github.com/adamcaudill/libsodium-net)
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* NodeJS: [node-sodium](https://github.com/paixaop/node-sodium)
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* Objective C: [NAChloride](https://github.com/gabriel/NAChloride)
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* Ocaml: [ocaml-sodium](https://github.com/dsheets/ocaml-sodium)
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* Perl: [Crypto-Sodium](https://github.com/mgregoro/Crypt-Sodium)
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* Pharo/Squeak: [Crypto-NaCl](http://www.eighty-twenty.org/index.cgi/tech/smalltalk/nacl-for-squeak-and-pharo-20130601.html)
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* PHP: [PHP-Sodium](https://github.com/alethia7/php-sodium)
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* PHP: [libsodium-php](https://github.com/jedisct1/libsodium-php)
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* Python: [PyNaCl](https://github.com/dstufft/pynacl)
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* Python: [PySodium](https://github.com/stef/pysodium)
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* Racket: part of [CRESTaceans](https://github.com/mgorlick/CRESTaceans/tree/master/bindings/libsodium)
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* Ruby: [RbNaCl](https://github.com/cryptosphere/rbnacl)
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* Ruby: [Sodium](https://github.com/stouset/sodium)
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* Rust: [Sodium Oxide](https://github.com/dnaq/sodiumoxide)
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## CurveCP
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CurveCP tools are part of a different project,
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[libchloride](https://github.com/jedisct1/libchloride).
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If you are interested in an embeddable CurveCP implementation, take a
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look at [libcurvecpr](https://github.com/impl/libcurvecpr).
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## Mailing list
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A mailing-list is available to discuss libsodium.
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In order to join, just send a random mail to `sodium-subscribe` {at}
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`pureftpd`{dot}`org`.
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## License
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[ISC license](http://en.wikipedia.org/wiki/ISC_license).
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See the `COPYING` file for details, `AUTHORS` for designers and
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implementors, and `THANKS` for contributors.
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