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zinc: introduce minimal cryptography libraryzinc

Zinc stands for "Zinc Is Not crypto/" or "Zinc Is Nice Crypto" or "Zinc Is New crypto/" or maybe just "Zx2c4's INsane Cryptolib." It's also short, easy to type, and plays nicely with the recent trend of naming crypto libraries after elements. The guiding principle is "don't overdo it". It's less of a library and more of a directory tree for organizing well-curated direct implementations of cryptography primitives. Zinc is a new cryptography API that is much more minimal and lower-level than the current one. It intends to complement it and provide a basis upon which the current crypto API might build, and perhaps someday Zinc may altogether supplant the current crypto API. It is motivated by three primary observations in crypto API design: * Highly composable "cipher modes" and related abstractions from 90s cryptographers did not turn out to be as terrific an idea as hoped, leading to a host of API misuse problems. * Most programmers are afraid of crypto code, and so prefer to integrate it into libraries in a highly abstracted manner, so as to shield themselves from implementation details. Cryptographers, on the other hand, prefer simple direct implementations, which they're able to verify for high assurance and optimize in accordance with their expertise. * Overly abstracted and flexible cryptography APIs lead to a host of dangerous problems and performance issues. The kernel is in the business usually not of coming up with new uses of crypto, but rather implementing various constructions, which means it essentially needs a library of primitives, not a highly abstracted enterprise-ready pluggable system, with a few particular exceptions. This last observation has seen itself play out several times over and over again within the kernel: * The perennial move of actual primitives away from crypto/ and into lib/, so that users can actually call these functions directly with no overhead and without lots of allocations, function pointers, string specifier parsing, and general clunkiness. For example: sha256, chacha20, siphash, sha1, and so forth live in lib/ rather than in crypto/. Zinc intends to stop the cluttering of lib/ and introduce these direct primitives into their proper place, lib/zinc/. * An abundance of misuse bugs with the present crypto API that have been very unpleasant to clean up. * A hesitance to even use cryptography, because of the overhead and headaches involved in accessing the routines. Zinc goes in a rather different direction. Rather than providing a thoroughly designed and abstracted API, Zinc gives you simple functions, which implement some primitive, or some particular and specific construction of primitives. It is not dynamic in the least, though one could imagine implementing a complex dynamic dispatch mechanism (such as the current crypto API) on top of these basic functions. After all, dynamic dispatch is usually needed for applications with cipher agility, such as IPsec, dm-crypt, AF_ALG, and so forth, and the existing crypto API will continue to play that role. However, Zinc will provide a non- haphazard way of directly utilizing crypto routines in applications that do have neither need nor desire for abstraction and dynamic dispatch. It also organizes the implementations in a simple, straight-forward, and direct manner, making it enjoyable and intuitive to work on. Rather than moving optimized assembly implementations into arch/, it keeps them all together in lib/zinc/, making it simple and obvious to compare and contrast what's happening. This is, notably, exactly what the lib/raid6/ tree does, and that seems to work out rather well. It's also the pattern of most successful crypto libraries. The architecture- specific glue-code is made a part of each translation unit, rather than being in a separate one, so that generic and architecture-optimized code are combined at compile-time and incompatibility branches compiled out by the optimizer. All implementations have been extensively tested and fuzzed, and are selected for their quality, trustworthiness, and performance. Wherever possible and performant, formally verified implementations are used, such as those from HACL* [1] and Fiat-Crypto [2]. The routines also take special care to zero out secrets using memzero_explicit (and future work is planned to have gcc do this more reliably and performantly with compiler plugins). The performance of the selected implementations is state-of-the-art and unrivaled. Each implementation also comes with extensive self-tests and crafted test vectors, pulled from various places such as Wycheproof [9]. Regularity of function signatures is important, so that users can easily "guess" the name of the function they want. Though, individual primitives are oftentimes not trivially interchangeable, having been designed for different things and requiring different parameters and semantics, and so the function signatures they provide will directly reflect the realities of the primitives' usages, rather than hiding it behind (inevitably leaky) abstractions. Also, in contrast to the current crypto API, Zinc functions can work on stack buffers, and can be called with different keys, without requiring allocations or locking. SIMD is used automatically when available, though some routines may benefit from either having their SIMD disabled for particular invocations, or to have the SIMD initialization calls amortized over several invocations of the function, and so Zinc provides helpers and function signatures enabling that. More generally, Zinc provides function signatures that allow just what is required by the various callers. This isn't to say that users of the functions will be permitted to pollute the function semantics with weird particular needs, but we are trying very hard not to overdo it, and that means looking carefully at what's actually necessary, and doing just that, and not much more than that. Remember: practicality and cleanliness rather than over-zealous infrastructure. Zinc provides also an opening for the best implementers in academia to contribute their time and effort to the kernel, by being sufficiently simple and inviting. In discussing this commit with some of the best and brightest over the last few years, there are many who are eager to devote rare talent and energy to this effort. Following the merging of this, I expect for first the primitives that currently exist in lib/ to work their way into lib/zinc/, after intense scrutiny of each implementation, potentially replacing them with either formally-verified implementations, or better studied and faster state-of-the-art implementations. In a phase after that, I envision that certain instances from crypto/ will want to rebase themselves to simply be abstracted crypto API wrappers using the lower level Zinc functions. This is already what various crypto/ implementations do with the existing code in lib/. As Zinc is simply library code, its config options are un-menued, with the exception of CONFIG_ZINC_DEBUG, which enables various selftests and BUG_ONs. [1] [2] [3] [4] [5] [6] [7] [8] [9] Signed-off-by: Jason A. Donenfeld <> Cc: Andy Lutomirski <> Cc: Greg KH <> Cc: Samuel Neves <> Cc: D. J. Bernstein <> Cc: Tanja Lange <> Cc: Jean-Philippe Aumasson <> Cc:

6 files changed, 70 insertions, 0 deletions

@@ -15859,6 +15859,14 @@ Q:

S: Maintained

F: drivers/media/dvb-frontends/zd1301_demod*


+M: Jason A. Donenfeld <>

+M: Samuel Neves <>

+S: Maintained

+F: lib/zinc/

+F: include/zinc/




M: Dan Streetman <>


@@ -478,6 +478,8 @@ config GLOB_SELFTEST

module load) by a small amount, so you're welcome to play with

it, but you probably don't need it.

+source "lib/zinc/Kconfig"



# Netlink attribute parsing support is select'ed if needed


@@ -211,6 +211,8 @@ obj-$(CONFIG_PERCPU_TEST) += percpu_test.o

obj-$(CONFIG_ASN1) += asn1_decoder.o

+obj-$(CONFIG_ZINC) += zinc/


obj-$(CONFIG_FONT_SUPPORT) += fonts/

obj-$(CONFIG_PRIME_NUMBERS) += prime_numbers.o

@@ -0,0 +1,20 @@

+config ZINC

+ tristate


+ select VFP

+ select VFPv3

+ select NEON



+config ZINC_DEBUG

+ bool "Zinc cryptography library debugging and self-tests"

+ depends on ZINC

+ help

+ This builds a series of self-tests for the Zinc crypto library, which

+ help diagnose any cryptographic algorithm implementation issues that

+ might be at the root cause of potential bugs. It also adds various

+ debugging traps.


+ Unless you're developing and testing cryptographic routines, or are

+ especially paranoid about correctness on your hardware, you may say

+ N here.

@@ -0,0 +1,7 @@

+ccflags-y := -O3

+ccflags-y += -Wframe-larger-than=8192

+ccflags-y += -D'pr_fmt(fmt)=KBUILD_MODNAME ": " fmt'


+zinc-y += main.o


+obj-$(CONFIG_ZINC) := zinc.o

@@ -0,0 +1,31 @@

+/* SPDX-License-Identifier: GPL-2.0

+ *

+ * Copyright (C) 2015-2018 Jason A. Donenfeld <>. All Rights Reserved.

+ */


+#include <linux/init.h>

+#include <linux/module.h>



+#define selftest(which) do { \

+ if (!which ## _selftest()) \


+} while (0)


+#define selftest(which)



+static int __init mod_init(void)


+ return 0;



+static void __exit mod_exit(void)







+MODULE_DESCRIPTION("Zinc cryptography library");

+MODULE_AUTHOR("Jason A. Donenfeld <>");