lib25519: People

lib25519 draws on many previous implementations listed below, plus new speedups from Kaushik Nath and new infrastructure work and factoring from Daniel J. Bernstein. Nath's work on this project was initially funded through the Internet Hardening Fund, a fund established by NLnet with financial support from the Netherlands Ministry of Economic Affairs and Climate Policy, and received further funding through the NGI0 Entrust Fund, another fund from NLnet established with financial support from the European Commission's Next Generation Internet program.

Some code was originally copied from public-domain code in the SUPERCOP benchmarking framework. See https://bench.cr.yp.to/supercop.html for SUPERCOP releases. The following small changes from code available in SUPERCOP are made in lib25519 without further comment:

Returning void rather than int for functions that never fail in lib25519.
Message lengths long long rather than unsigned long long.
Defining various constants in .c files (to simplify PIC handling) instead of .S files.
Moving some C files to shared-*.c (which in lib25519 means that these files are compiled by only one compiler).
Using CRYPTO_SHARED_NAMESPACE rather than CRYPTO_NAMESPACE for symbols defined in *.S and shared-*.c.
Adding various linker define and linker use lines.

Larger changes from code in SUPERCOP, such as new code divisions across lib25519 primitives, are indicated below.

Sources of Curve25519 software (this is not a comprehensive list, just the software that lib25519 is derived from):

Daniel J. Bernstein. "Curve25519: new Diffie-Hellman speed records." Pages 207–228 in Public key cryptography—PKC 2006, 9th international conference on theory and practice in public-key cryptography, New York, NY, USA, April 24–26, 2006, proceedings, edited by Moti Yung, Yevgeniy Dodis, Aggelos Kiayias, Tal Malkin, Lecture Notes in Computer Science 3958, Springer, 2006, ISBN 3-540-33851-9.

This is the source of the Curve25519 design, the X25519 design, and various speedups. Most of the software from that paper is specific to a variety of 32-bit platforms (radix 2^25.5 or radix 2^21.25), but the portable supercop/crypto_scalarmult/curve25519/ref10 (radix 2^25.5) is derived from this.

lib25519/crypto_nP/montgomery25519/ref10 starts with supercop/crypto_scalarmult/curve25519/ref10, and tweaks the API to provide crypto_nP instead of crypto_scalarmult. Inversion is factored out, producing crypto_pow/inv25519/ref10. The trivial crypto_scalarmult_base wrapper is factored out, producing crypto_nG/montgomery25519/ref/base.c; lib25519 has faster nG functions, but intentionally provides ref for situations where speed is outweighed by simplicity, assurance, code size, etc.
supercop/crypto_scalarmult/curve25519/donna_c64 (radix 2⁵¹) from Adam Langley.

lib25519/crypto_nP/montgomery25519/donna_c64 starts from this and tweaks the API to provide crypto_nP instead of crypto_scalarmult (and removes crypto_scalarmult_base). crypto_pow/inv25519/donna_c64 is factored out.
Daniel J. Bernstein, Niels Duif, Tanja Lange, Peter Schwabe, Bo-Yin Yang. "High-speed high-security signatures." Pages 124–142 in Cryptographic hardware and embedded systems—CHES 2011, 13th international workshop, Nara, Japan, September 28–October 1, 2011, proceedings, edited by Bart Preneel, Tsuyoshi Takagi, Lecture Notes in Computer Science 6917, Springer, 2011, ISBN 978-3-642-23950-2. Journal version: Journal of Cryptographic Engineering 2 (2012), 77–89.

This is the source of the Ed25519 design and various X25519/Ed25519 speedups for 64-bit Intel/AMD platforms, in particular producing supercop/crypto_{scalarmult/curve,sign/ed}25519/amd64-{51,64}* (radix 2⁵¹ and radix 2⁶⁴ respectively). Peter Schwabe led the implementation work.

lib25519/crypto_nP/montgomery25519/amd64-51 starts from supercop/crypto_scalarmult/curve25519/amd64-51 and tweaks the API to provide crypto_nP instead of crypto_scalarmult (and removes crypto_scalarmult_base). crypto_nG/merged25519/amd64-51 (for fixed-base-point multiplication), crypto_mGnP/ed25519/amd64-51 (for double-scalar multiplication), and crypto_sign/ed25519/amd64 (for the remaining signing components) factor supercop/crypto_sign/ed25519/amd64-51 into smaller pieces. crypto_pow/inv25519/amd64-51 is also factored out. SMALLTABLES support is removed. Support for batch verification is removed, although it could reappear in a subsequent lib25519 release.

Similar comments apply to amd64-64 and ref10. A compiler warning is eliminated (window size 64 in amd64-64-24k/sc25519.h).
Tung Chou. "Sandy2x: New Curve25519 Speed Records." SAC 2015.

This is the source of various X25519 speedups using 256-bit vector instructions, specifically AVX vector instructions in Intel's Sandy Bridge, in particular producing supercop/crypto_scalarmult/curve25519/sandy2x (radix 2^25.5).

lib25519/crypto_{nP,nG}/montgomery25519/sandy2x start from supercop/crypto_scalarmult/curve25519/sandy2x, and tweak the API to provide crypto_nP and crypto_nG instead of crypto_scalarmult and crypto_scalarmult_base respectively. The top bit of the incoming point is cleared. crypto_pow/inv25519/sandy2x is factored out.
Kaushik Nath and Palash Sarkar, "Efficient arithmetic in (pseudo-)Mersenne prime order fields", Advances in Mathematics of Communications 16 (2022), pages 303–348. Original release:
- https://github.com/kn-cs/pmp-farith/tree/master/gf-p2-255-19/SL
- https://github.com/kn-cs/pmp-farith/tree/master/gf-p2-255-19/USL1
The SL software is the source of various speedups to the amd64-64 software, producing the maa4 versions of fe25519_mul.S, fe25519_square.S, and fe25519_nsquare.S. These .S files are used inside the following lib25519 directories:
- crypto_mGnP/ed25519/amd64-avx2-10l-maa4
- crypto_mGnP/ed25519/amd64-avx2-9l-maa4
- crypto_mGnP/ed25519/amd64-maa4
- crypto_nG/merged25519/amd64-avx2-10l-maa4
- crypto_nG/merged25519/amd64-avx2-9l-maa4
- crypto_nG/merged25519/amd64-maa4
- crypto_nP/montgomery25519/amd64-avx2-hey10l-maa4
- crypto_nP/montgomery25519/amd64-avx2-hey9l-maa4
- crypto_nP/montgomery25519/amd64-avx2-ns10l-maa4
- crypto_nP/montgomery25519/amd64-avx2-ns9l-maa4
- crypto_nP/montgomery25519/amd64-maa4
- crypto_pow/inv25519/amd64-maa4
The USL software is the source of various speedups to the amd64-51 software, producing the maa5 versions of fe25519_mul.S and fe25519_nsquare.S. These .S files are used inside the following lib25519 directories:
- crypto_nP/montgomery25519/amd64-avx2-hey10l-maa5
- crypto_nP/montgomery25519/amd64-avx2-hey9l-maa5
- crypto_nP/montgomery25519/amd64-avx2-ns10l-maa5
- crypto_nP/montgomery25519/amd64-avx2-ns9l-maa5
- crypto_pow/inv25519/amd64-maa5
Kaushik Nath and Palash Sarkar, "Security and efficiency trade-offs for elliptic curve Diffie-Hellman at the 128-bit and 224-bit security levels." J. Cryptogr. Eng. 12(1): 107-121 (2022). Original release:
- https://github.com/kn-cs/x25519/tree/master/intel64-mxaa-4limb
- https://github.com/kn-cs/x25519
This mxaa-4limb software is the source of various speedups to maa4 on CPUs supporting BMI2 instructions (e.g., Intel Haswell from 2013), in particular producing the mxaa versions of fe25519_mul.S and fe25519_nsquare.S. These .S files are used inside the following lib25519 directories:
- crypto_mGnP/ed25519/amd64-avx2-10l-mxaa
- crypto_mGnP/ed25519/amd64-avx2-9l-mxaa
- crypto_mGnP/ed25519/amd64-mxaa
- crypto_nG/merged25519/amd64-avx2-10l-mxaa
- crypto_nG/merged25519/amd64-avx2-9l-mxaa
- crypto_nG/merged25519/amd64-mxaa
- crypto_nP/montgomery25519/amd64-avx2-hey10l-mxaa
- crypto_nP/montgomery25519/amd64-avx2-hey9l-mxaa
- crypto_nP/montgomery25519/amd64-avx2-ns10l-mxaa
- crypto_nP/montgomery25519/amd64-avx2-ns9l-mxaa
- crypto_nP/montgomery25519/amd64-mxaa
- crypto_pow/inv25519/amd64-mxaa
This software is also the source of the following three different Montgomery-ladder functions, where the third also builds on the maax work listed below:
- crypto_nP/montgomery25519/amd64-maa4/mladder.S
- crypto_nP/montgomery25519/amd64-mxaa/mladder.S
- crypto_nP/montgomery25519/amd64-maax/mladder.S
Kaushik Nath and Palash Sarkar, "Efficient arithmetic in (pseudo-)Mersenne prime order fields", Advances in Mathematics of Communications 16 (2022), pages 303–348. Original release:
- https://github.com/kn-cs/pmp-farith/tree/master/gf-p2-255-19/SLDCC
This is the source of various speedups to mxaa on CPUs that also support ADX instructions (e.g., Intel Broadwell from 2014), in particular producing the maax versions of fe25519_mul.S, fe25519_square.S, and fe25519_nsquare.S. These .S files are used inside the following lib25519 directories:
- crypto_mGnP/ed25519/amd64-avx2-10l-maax
- crypto_mGnP/ed25519/amd64-avx2-9l-maax
- crypto_mGnP/ed25519/amd64-avx512ifma-5l-maax
- crypto_mGnP/ed25519/amd64-maax
- crypto_nG/merged25519/amd64-avx2-10l-maax
- crypto_nG/merged25519/amd64-avx2-9l-maax
- crypto_nG/merged25519/amd64-avx512ifma-5l-maax
- crypto_nG/merged25519/amd64-maax
- crypto_nP/montgomery25519/amd64-avx2-hey10l-maax
- crypto_nP/montgomery25519/amd64-avx2-hey9l-maax
- crypto_nP/montgomery25519/amd64-avx2-ns10l-maax
- crypto_nP/montgomery25519/amd64-avx2-ns9l-maax
- crypto_nP/montgomery25519/amd64-avx512-hey10l-maax
- crypto_nP/montgomery25519/amd64-avx512-hey9l-maax
- crypto_nP/montgomery25519/amd64-avx512-ns10l-maax
- crypto_nP/montgomery25519/amd64-avx512-ns9l-maax
- crypto_nP/montgomery25519/amd64-avx512ifma-hey5l-maax
- crypto_nP/montgomery25519/amd64-avx512ifma-ns5l-maax
- crypto_nP/montgomery25519/amd64-maax
- crypto_pow/inv25519/amd64-maax
Kaushik Nath and Palash Sarkar, "Efficient 4-Way Vectorizations of the Montgomery Ladder". IEEE Trans. Computers 71(3): 712-723 (2022). Original release:
- https://github.com/kn-cs/vec-ladder/tree/master/Curve25519
This is the source of the hey10l (radix 2^25.5), hey9l (radix 2²⁹), ns10l (radix 2^25.5), and ns9l (radix 2²⁹) versions of mladder.S for CPUs that also support 256-bit AVX2 instructions (e.g., Intel Haswell from 2013). In lib25519, these four .S files are used in 16 directories:
- crypto_nP/montgomery25519/amd64-avx2-hey10l-{maa4,maa5,maax,mxaa}
- crypto_nP/montgomery25519/amd64-avx2-hey9l-{maa4,maa5,maax,mxaa}
- crypto_nP/montgomery25519/amd64-avx2-ns10l-{maa4,maa5,maax,mxaa}
- crypto_nP/montgomery25519/amd64-avx2-ns9l-{maa4,maa5,maax,mxaa}
Kaushik Nath, new Montgomery-ladder code new in lib25519 (no paper yet) for CPUs supporting AVX-512 instructions (e.g., Intel Skylake-X from 2017). These are six files in lib25519:
- crypto_nP/montgomery25519/amd64-avx512-hey10l-maax
- crypto_nP/montgomery25519/amd64-avx512-hey9l-maax
- crypto_nP/montgomery25519/amd64-avx512-ns10l-maax
- crypto_nP/montgomery25519/amd64-avx512-ns9l-maax
- crypto_nP/montgomery25519/amd64-avx512ifma-hey5l-maax
- crypto_nP/montgomery25519/amd64-avx512ifma-ns5l-maax
Kaushik Nath, nine versions of fixed-base-point scalar-multiplication code new in lib25519 (no paper yet) for various platforms:
- crypto_nG/merged25519/amd64-avx2-10l-maa4/ge25519_base.S
- crypto_nG/merged25519/amd64-avx2-10l-maax/ge25519_base.S
- crypto_nG/merged25519/amd64-avx2-10l-mxaa/ge25519_base.S
- crypto_nG/merged25519/amd64-avx2-9l-maa4/ge25519_base.S
- crypto_nG/merged25519/amd64-avx2-9l-maax/ge25519_base.S
- crypto_nG/merged25519/amd64-avx2-9l-mxaa/ge25519_base.S
- crypto_nG/merged25519/amd64-avx512ifma-5l-maax/ge25519_base.S
- crypto_nG/merged25519/amd64-maa4/ge25519_base.S
- crypto_nG/merged25519/amd64-maax/ge25519_base.S
- crypto_nG/merged25519/amd64-mxaa/ge25519_base.S
Kaushik Nath, ten versions of double-scalar-multiplication code new in lib25519 (no paper yet) for various platforms. Each version has precompute.S and process.S:
- crypto_mGnP/ed25519/amd64-avx2-10l-maa4/ge25519_double_scalarmult_precompute.S
- crypto_mGnP/ed25519/amd64-avx2-10l-maax/ge25519_double_scalarmult_precompute.S
- crypto_mGnP/ed25519/amd64-avx2-10l-mxaa/ge25519_double_scalarmult_precompute.S
- crypto_mGnP/ed25519/amd64-avx2-9l-maa4/ge25519_double_scalarmult_precompute.S
- crypto_mGnP/ed25519/amd64-avx2-9l-maax/ge25519_double_scalarmult_precompute.S
- crypto_mGnP/ed25519/amd64-avx2-9l-mxaa/ge25519_double_scalarmult_precompute.S
- crypto_mGnP/ed25519/amd64-avx512ifma-5l-maax/ge25519_double_scalarmult_precompute.S
- crypto_mGnP/ed25519/amd64-maa4/ge25519_double_scalarmult_precompute.S
- crypto_mGnP/ed25519/amd64-maax/ge25519_double_scalarmult_precompute.S
- crypto_mGnP/ed25519/amd64-mxaa/ge25519_double_scalarmult_precompute.S
- crypto_mGnP/ed25519/amd64-avx2-10l-maa4/ge25519_double_scalarmult_process.S
- crypto_mGnP/ed25519/amd64-avx2-10l-maax/ge25519_double_scalarmult_process.S
- crypto_mGnP/ed25519/amd64-avx2-10l-mxaa/ge25519_double_scalarmult_process.S
- crypto_mGnP/ed25519/amd64-avx2-9l-maa4/ge25519_double_scalarmult_process.S
- crypto_mGnP/ed25519/amd64-avx2-9l-maax/ge25519_double_scalarmult_process.S
- crypto_mGnP/ed25519/amd64-avx2-9l-mxaa/ge25519_double_scalarmult_process.S
- crypto_mGnP/ed25519/amd64-avx512ifma-5l-maax/ge25519_double_scalarmult_process.S
- crypto_mGnP/ed25519/amd64-maa4/ge25519_double_scalarmult_process.S
- crypto_mGnP/ed25519/amd64-maax/ge25519_double_scalarmult_process.S
- crypto_mGnP/ed25519/amd64-mxaa/ge25519_double_scalarmult_process.S
Kaushik Nath, batch scalar-multiplication code new in lib25519 (no paper yet):
- crypto_nPbatch/montgomery25519/amd64-avx512ifma-8x1

Almost all of the crypto_pow/inv25519 implementations use exponentiation, but there is also a different implementation from the following source:

Daniel J. Bernstein, Bo-Yin Yang. "Fast constant-time gcd computation and modular inversion." IACR Transactions on Cryptographic Hardware and Embedded Systems 2019 issue 3 (2019), 340–398.

This is the source of the "safegcd" algorithm and software. Further speedups (no paper yet; ideas from Peter Dettman, Gregory Maxwell, and Pieter Wuille) have produced the "inverse25519skylake" software available here: https://gcd.cr.yp.to/software.html

lib25519/crypto_pow/inv25519/amd64-safegcd is inverse25519skylake, tweaked to provide the crypto_pow API and to clear the top bit of the input.

For lower-layer SHA-512 functions:

Daniel J. Bernstein, supercop/crypto_hash*/sha512/*. In lib25519, some unused variables are removed in crypto_hashblocks/sha512/avx to eliminate compiler warnings.

Most of the lib25519 infrastructure, such as the run-time implementation selector automatically guided by CPU type and previous benchmarks, is new in lib25519 from Daniel J. Bernstein. Portions of autogen/speed (generating lib25519-speed.c) and autogen/test (generating lib25519-test.c) are based on benchmarking software and test software in SUPERCOP by Daniel J. Bernstein. The symmetric-cryptography code for generating pseudorandom test inputs and hashing test outputs is adapted from TweetNaCl, a library by Daniel J. Bernstein, Wesley Janssen, Tanja Lange, and Peter Schwabe.

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