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|
package entropy
import (
crand "crypto/rand"
"crypto/sha512"
"encoding/binary"
"errors"
"fmt"
"io"
"sync"
)
const blockSize = sha512.Size
var ErrExternalEntropyRequired = errors.New("external entropy source required")
type HybridOptions struct {
RequireExternal bool
}
type HybridReader struct {
base io.Reader
external io.Reader
requireExternal bool
mu sync.Mutex
counter uint64
degraded bool
degradeErr error
buffer []byte
}
func NewHybridReader(base io.Reader, external io.Reader, opts HybridOptions) (*HybridReader, error) {
if base == nil {
base = crand.Reader
}
if external == nil {
return nil, ErrExternalEntropyRequired
}
return &HybridReader{
base: base,
external: external,
requireExternal: opts.RequireExternal,
}, nil
}
func (r *HybridReader) Read(p []byte) (int, error) {
if len(p) == 0 {
return 0, nil
}
r.mu.Lock()
defer r.mu.Unlock()
written := 0
for written < len(p) {
if len(r.buffer) > 0 {
n := copy(p[written:], r.buffer)
written += n
r.buffer = r.buffer[n:]
continue
}
block, err := r.nextBlockLocked()
if err != nil {
return written, err
}
n := copy(p[written:], block[:])
written += n
if n < len(block) {
r.buffer = append(r.buffer[:0], block[n:]...)
}
}
return written, nil
}
func (r *HybridReader) Degraded() bool {
r.mu.Lock()
defer r.mu.Unlock()
return r.degraded
}
func (r *HybridReader) DegradeError() error {
r.mu.Lock()
defer r.mu.Unlock()
return r.degradeErr
}
func (r *HybridReader) nextBlockLocked() ([blockSize]byte, error) {
var base [blockSize]byte
if _, err := io.ReadFull(r.base, base[:]); err != nil {
return [blockSize]byte{}, fmt.Errorf("read OS CSPRNG: %w", err)
}
if r.degraded {
return base, nil
}
var external [blockSize]byte
if _, err := io.ReadFull(r.external, external[:]); err != nil {
if r.requireExternal {
return [blockSize]byte{}, fmt.Errorf("read external entropy: %w", err)
}
r.degraded = true
r.degradeErr = err
return base, nil
}
var counter [8]byte
binary.BigEndian.PutUint64(counter[:], r.counter)
r.counter++
h := sha512.New()
h.Write([]byte("qpass hybrid entropy v1\x00"))
h.Write(counter[:])
h.Write(base[:])
h.Write(external[:])
var out [blockSize]byte
copy(out[:], h.Sum(nil))
return out, nil
}
func InstallGlobal(reader io.Reader) func() {
if reader == nil {
reader = crand.Reader
}
previous := crand.Reader
crand.Reader = reader
return func() {
crand.Reader = previous
}
}
|
