TweetNaCl is a compact reimplementation of the NaCl library by Daniel J. Bernstein, Bernard van Gastel, Wesley Janssen, Tanja Lange, Peter Schwabe and Sjaak Smetsers. The library is less than 20 KB in size and provides 25 of the NaCl library functions.
The compact library uses curve25519, XSalsa20, Poly1305 and SHA-512 as default primitives, and includes both x25519 key exchange and ed25519 signatures. The complete list of functions can be found in TweetNaCl: A crypto library in 100 tweets (20140917), Table 1, page 5.
Crypto++ retained the function names and signatures but switched to data types provided by <stdint.h> to promote interoperability with Crypto++ and avoid size problems on platforms like Cygwin. For example, NaCl typdef'd u64 as an unsigned long long, but Cygwin, MinGW and MSYS are LP64 systems (not LLP64 systems). In addition, Crypto++ was missing NaCl's signed 64-bit integer i64.
Crypto++ enforces the 0-key restriction due to small points. The TweetNaCl library allowed the 0-keys to small points. Also see RFC 7748, Elliptic Curves for Security, Section 6.
TweetNaCl is well written but not well optimized. It runs 2x to 3x slower than optimized routines from libsodium. However, the library is still 2x to 4x faster than the algorithms NaCl was designed to replace.
The Crypto++ wrapper for TweetNaCl requires OS features. That is, NO_OS_DEPENDENCE cannot be defined. It is due to TweetNaCl's internal function randombytes. Crypto++ used DefaultAutoSeededRNG within randombytes, so OS integration must be enabled. You can use another generator like RDRAND to avoid the restriction.
This is initial testing support for N4713, "Working Draft, Standard for Programming Language C++". We know GCC uses -std=c++20 and -std=gnu++20, so we can start testing things
Add tests for Support for Control-flow Enforcement Technology (CET). This is an upcoming processor feature. We want to be out in front of breaks to our inline assembly
We determine machine capabilities by performing an os/platform *query* first, like getauxv(). If the *query* fails, we move onto a cpu *probe*. The cpu *probe* tries to exeute an instruction and then catches a SIGILL on Linux or the exception EXCEPTION_ILLEGAL_INSTRUCTION on Windows. Some OSes fail to hangle a SIGILL gracefully, like Apple OSes. Apple machines corrupt memory and variables around the probe.
Jeffrey Walton