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// Copyright 2010 The Go Authors.  All rights reserved.

// Use of this source code is governed by a BSD-style

// license that can be found in the LICENSE file.

// Windows cryptographically secure pseudorandom number

// generator.

package rand

import (

        "os"

        "sync"

        "syscall"

)

// Implemented by using Windows CryptoAPI 2.0.

func init() { Reader = &rngReader{} }

// A rngReader satisfies reads by reading from the Windows CryptGenRandom API.

type rngReader struct {

        prov syscall.Handle

        mu   sync.Mutex

}

func (r *rngReader) Read(b []byte) (n int, err error) {

        r.mu.Lock()

        if r.prov == 0 {

                const provType = syscall.PROV_RSA_FULL

                const flags = syscall.CRYPT_VERIFYCONTEXT | syscall.CRYPT_SILENT

                err := syscall.CryptAcquireContext(&r.prov, nil, nil, provType, flags)

                if err != nil {

                        r.mu.Unlock()

                        return 0, os.NewSyscallError("CryptAcquireContext", err)

                }

        }

        r.mu.Unlock()

        err = syscall.CryptGenRandom(r.prov, uint32(len(b)), &b[0])

        if err != nil {

                return 0, os.NewSyscallError("CryptGenRandom", err)

        }

        return len(b), nil

}