remove MixEntropy (#3278)

* remove MixEntropy

* changelog

crypto/random.go

@@ -1,42 +1,11 @@
 package crypto
 
 import (
-	"crypto/cipher"
 	crand "crypto/rand"
-	"crypto/sha256"
 	"encoding/hex"
 	"io"
-	"sync"
-
-	"golang.org/x/crypto/chacha20poly1305"
 )
 
-// NOTE: This is ignored for now until we have time
-// to properly review the MixEntropy function - https://github.com/tendermint/tendermint/issues/2099.
-//
-// The randomness here is derived from xoring a chacha20 keystream with
-// output from crypto/rand's OS Entropy Reader. (Due to fears of the OS'
-// entropy being backdoored)
-//
-// For forward secrecy of produced randomness, the internal chacha key is hashed
-// and thereby rotated after each call.
-var gRandInfo *randInfo
-
-func init() {
-	gRandInfo = &randInfo{}
-
-	// TODO: uncomment after reviewing MixEntropy -
-	// https://github.com/tendermint/tendermint/issues/2099
-	// gRandInfo.MixEntropy(randBytes(32)) // Init
-}
-
-// WARNING: This function needs review - https://github.com/tendermint/tendermint/issues/2099.
-// Mix additional bytes of randomness, e.g. from hardware, user-input, etc.
-// It is OK to call it multiple times.  It does not diminish security.
-func MixEntropy(seedBytes []byte) {
-	gRandInfo.MixEntropy(seedBytes)
-}
-
 // This only uses the OS's randomness
 func randBytes(numBytes int) []byte {
 	b := make([]byte, numBytes)
@@ -52,19 +21,6 @@ func CRandBytes(numBytes int) []byte {
 	return randBytes(numBytes)
 }
 
-/* TODO: uncomment after reviewing MixEntropy - https://github.com/tendermint/tendermint/issues/2099
-// This uses the OS and the Seed(s).
-func CRandBytes(numBytes int) []byte {
-	return randBytes(numBytes)
-		b := make([]byte, numBytes)
-		_, err := gRandInfo.Read(b)
-		if err != nil {
-			panic(err)
-		}
-		return b
-}
-*/
-
 // CRandHex returns a hex encoded string that's floor(numDigits/2) * 2 long.
 //
 // Note: CRandHex(24) gives 96 bits of randomness that
@@ -77,63 +33,3 @@ func CRandHex(numDigits int) string {
 func CReader() io.Reader {
 	return crand.Reader
 }
-
-/* TODO: uncomment after reviewing MixEntropy - https://github.com/tendermint/tendermint/issues/2099
-// Returns a crand.Reader mixed with user-supplied entropy
-func CReader() io.Reader {
-	return gRandInfo
-}
-*/
-
-//--------------------------------------------------------------------------------
-
-type randInfo struct {
-	mtx       sync.Mutex
-	seedBytes [chacha20poly1305.KeySize]byte
-	chacha    cipher.AEAD
-	reader    io.Reader
-}
-
-// You can call this as many times as you'd like.
-// XXX/TODO: review - https://github.com/tendermint/tendermint/issues/2099
-func (ri *randInfo) MixEntropy(seedBytes []byte) {
-	ri.mtx.Lock()
-	defer ri.mtx.Unlock()
-	// Make new ri.seedBytes using passed seedBytes and current ri.seedBytes:
-	// ri.seedBytes = sha256( seedBytes || ri.seedBytes )
-	h := sha256.New()
-	h.Write(seedBytes)
-	h.Write(ri.seedBytes[:])
-	hashBytes := h.Sum(nil)
-	copy(ri.seedBytes[:], hashBytes)
-	chacha, err := chacha20poly1305.New(ri.seedBytes[:])
-	if err != nil {
-		panic("Initializing chacha20 failed")
-	}
-	ri.chacha = chacha
-	// Create new reader
-	ri.reader = &cipher.StreamReader{S: ri, R: crand.Reader}
-}
-
-func (ri *randInfo) XORKeyStream(dst, src []byte) {
-	// nonce being 0 is safe due to never re-using a key.
-	emptyNonce := make([]byte, 12)
-	tmpDst := ri.chacha.Seal([]byte{}, emptyNonce, src, []byte{0})
-	// this removes the poly1305 tag as well, since chacha is a stream cipher
-	// and we truncate at input length.
-	copy(dst, tmpDst[:len(src)])
-	// hash seedBytes for forward secrecy, and initialize new chacha instance
-	newSeed := sha256.Sum256(ri.seedBytes[:])
-	chacha, err := chacha20poly1305.New(newSeed[:])
-	if err != nil {
-		panic("Initializing chacha20 failed")
-	}
-	ri.chacha = chacha
-}
-
-func (ri *randInfo) Read(b []byte) (n int, err error) {
-	ri.mtx.Lock()
-	n, err = ri.reader.Read(b)
-	ri.mtx.Unlock()
-	return
-}