github.com/remobjects/goldbaselibrary@v0.0.0-20230924164425-d458680a936b/Source/Gold/crypto/rand/rand_windows.go (about)

     1  // Copyright 2010 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Windows cryptographically secure pseudorandom number
     6  // generator.
     7  
     8  package rand
     9  
    10  import (
    11  	"os"
    12  	"sync"
    13  	"sync/atomic"
    14  	"syscall"
    15  	"time"
    16  )
    17  
    18  // Implemented by using Windows CryptoAPI 2.0.
    19  
    20  func init() { Reader = &rngReader{} }
    21  
    22  // A rngReader satisfies reads by reading from the Windows CryptGenRandom API.
    23  type rngReader struct {
    24  	used int32 // atomic; whether this rngReader has been used
    25  	prov syscall.Handle
    26  	mu   sync.Mutex
    27  }
    28  
    29  func (r *rngReader) Read(b []byte) (n int, err error) {
    30  	if atomic.CompareAndSwapInt32(&r.used, 0, 1) {
    31  		// First use of randomness. Start timer to warn about
    32  		// being blocked on entropy not being available.
    33  		t := time.AfterFunc(60*time.Second, warnBlocked)
    34  		defer t.Stop()
    35  	}
    36  	r.mu.Lock()
    37  	if r.prov == 0 {
    38  		const provType = syscall.PROV_RSA_FULL
    39  		const flags = syscall.CRYPT_VERIFYCONTEXT | syscall.CRYPT_SILENT
    40  		err := syscall.CryptAcquireContext(&r.prov, nil, nil, provType, flags)
    41  		if err != nil {
    42  			r.mu.Unlock()
    43  			return 0, os.NewSyscallError("CryptAcquireContext", err)
    44  		}
    45  	}
    46  	r.mu.Unlock()
    47  
    48  	if len(b) == 0 {
    49  		return 0, nil
    50  	}
    51  	err = syscall.CryptGenRandom(r.prov, uint32(len(b)), &b[0])
    52  	if err != nil {
    53  		return 0, os.NewSyscallError("CryptGenRandom", err)
    54  	}
    55  	return len(b), nil
    56  }