package main

import (
        "encoding/hex"
        "fmt"
        "io"
        "log"
        "os"
        "syscall"

        "golang.org/x/sys/unix"
)

func main() {
        log.SetFlags(log.Lshortfile)

        s, err := unix.Socket(unix.AF_ALG, unix.SOCK_SEQPACKET, 0)
        if err != nil {
                log.Fatal(err)
        }

        err = unix.Bind(s, &unix.SockaddrALG{
                Type: "hash",
                Name: "sha1",
        })
        if err != nil {
                log.Fatal(err)
        }

        nfd, _, e := syscall.Syscall(syscall.SYS_ACCEPT, uintptr(s), 0, 0)
        if e != 0 {
                log.Fatalf("errno:", e)
        }

        f := os.NewFile(nfd, "alg")
        io.Copy(f, os.Stdin)

        b := make([]byte, 20)
        if _, err := f.Read(b); err != nil {
                log.Fatal("read:", err)
        }

        fmt.Println(hex.EncodeToString(b))
}

$ echo "foo" | sha1sum                                                                                                                             
f1d2d2f924e986ac86fdf7b36c94bcdf32beec15  -
$ echo "foo" | ./afalg 
f1d2d2f924e986ac86fdf7b36c94bcdf32beec15

$ du -h ~/tmp/linux-4.10-rc7.tar.xz 
90M     /home/matt/tmp/linux-4.10-rc7.tar.xz
$ sha1sum ~/tmp/linux-4.10-rc7.tar.xz 
85cdcad0c06eef66f805ecce353bec9accbeecc5  /home/matt/tmp/linux-4.10-rc7.tar.xz
$ go test -v -bench=.
=== RUN   TestSHA1Equal
result: 85cdcad0c06eef66f805ecce353bec9accbeecc5
--- PASS: TestSHA1Equal (0.33s)
BenchmarkCryptoSHA1-4             200000              8012 ns/op
BenchmarkAFALGSHA1-4              200000              8786 ns/op
PASS
ok      github.com/mdlayher/afalg       7.653s