crypto/aes: AES cipher creation and encrypt / decrypt operations can be sped up significantly

[marten-seemann]

Go version

go version go1.21.4 darwin/arm64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/marten/Library/Caches/go-build'
GOENV='/Users/marten/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/marten/src/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/marten/src/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/Users/marten/bin/go1.21ex'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/Users/marten/bin/go1.21ex/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.21.4'
GCCGO='gccgo'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/q0/b5ynf00142l7bl9sp8y098zr0000gn/T/go-build341590646=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

I'm the maintainer of quic-go, and I'm working on reducing the allocations during the QUIC handshake (tracking issue).

What did you see happen?

The major source of allocations lies in the standard library, especially the crypto packages. Creating AES ciphers is part of this.

The allocations coming from the two slices embedded in aesCipher could easily be avoided:

go/src/crypto/aes/cipher.go

Lines 17 to 21 in b8ac61e

	// A cipher is an instance of AES encryption using a particular key.
	type aesCipher struct {
	enc []uint32
	dec []uint32
	}

These slices have lengths between 44 and 60 bytes, depending on the AES variant (AES-128, AES-192, AES-256). By replacing them with a fixed-size 60 element array (plus one length field), the number of allocations can be reduced significantly. This also reduces pointer chasing when encrypting / decrypting data.

What did you expect to see?

I'm going to submit a CL that implements this suggestion.

[gopherbot]

Change https://go.dev/cl/561080 mentions this issue: crypto/aes: speed up AES by reducing allocation

[Jorropo]

cc @FiloSottile @rolandshoemaker @golang/security as per https://dev.golang.org/owners

[mateusz834]

I've made a similar change before in CL CL 461078, but this seems better. I will abort that change.