Remove unused xsalsa20symmetric package. (#7691)

This package has no uses within Tendermint core.
PR https://github.com/cosmos/cosmos-sdk/pull/11027 replaces the use in
the Cosmos SDK.

A follow-up to #7689 and #7690.

crypto/xsalsa20symmetric/symmetric.go

@@ -1,54 +0,0 @@
-package xsalsa20symmetric
-
-import (
-	"errors"
-	"fmt"
-
-	"golang.org/x/crypto/nacl/secretbox"
-
-	"github.com/tendermint/tendermint/crypto"
-)
-
-// TODO, make this into a struct that implements crypto.Symmetric.
-
-const nonceLen = 24
-const secretLen = 32
-
-// secret must be 32 bytes long. Use something like Sha256(Bcrypt(passphrase))
-// The ciphertext is (secretbox.Overhead + 24) bytes longer than the plaintext.
-func EncryptSymmetric(plaintext []byte, secret []byte) (ciphertext []byte) {
-	if len(secret) != secretLen {
-		panic(fmt.Sprintf("Secret must be 32 bytes long, got len %v", len(secret)))
-	}
-	nonce := crypto.CRandBytes(nonceLen)
-	nonceArr := [nonceLen]byte{}
-	copy(nonceArr[:], nonce)
-	secretArr := [secretLen]byte{}
-	copy(secretArr[:], secret)
-	ciphertext = make([]byte, nonceLen+secretbox.Overhead+len(plaintext))
-	copy(ciphertext, nonce)
-	secretbox.Seal(ciphertext[nonceLen:nonceLen], plaintext, &nonceArr, &secretArr)
-	return ciphertext
-}
-
-// secret must be 32 bytes long. Use something like Sha256(Bcrypt(passphrase))
-// The ciphertext is (secretbox.Overhead + 24) bytes longer than the plaintext.
-func DecryptSymmetric(ciphertext []byte, secret []byte) (plaintext []byte, err error) {
-	if len(secret) != secretLen {
-		panic(fmt.Sprintf("Secret must be 32 bytes long, got len %v", len(secret)))
-	}
-	if len(ciphertext) <= secretbox.Overhead+nonceLen {
-		return nil, errors.New("ciphertext is too short")
-	}
-	nonce := ciphertext[:nonceLen]
-	nonceArr := [nonceLen]byte{}
-	copy(nonceArr[:], nonce)
-	secretArr := [secretLen]byte{}
-	copy(secretArr[:], secret)
-	plaintext = make([]byte, len(ciphertext)-nonceLen-secretbox.Overhead)
-	_, ok := secretbox.Open(plaintext[:0], ciphertext[nonceLen:], &nonceArr, &secretArr)
-	if !ok {
-		return nil, errors.New("ciphertext decryption failed")
-	}
-	return plaintext, nil
-}

crypto/xsalsa20symmetric/symmetric_test.go

@@ -1,40 +0,0 @@
-package xsalsa20symmetric
-
-import (
-	"testing"
-
-	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
-
-	"golang.org/x/crypto/bcrypt"
-
-	"github.com/tendermint/tendermint/crypto"
-)
-
-func TestSimple(t *testing.T) {
-
-	plaintext := []byte("sometext")
-	secret := []byte("somesecretoflengththirtytwo===32")
-	ciphertext := EncryptSymmetric(plaintext, secret)
-	plaintext2, err := DecryptSymmetric(ciphertext, secret)
-
-	require.NoError(t, err, "%+v", err)
-	assert.Equal(t, plaintext, plaintext2)
-}
-
-func TestSimpleWithKDF(t *testing.T) {
-
-	plaintext := []byte("sometext")
-	secretPass := []byte("somesecret")
-	secret, err := bcrypt.GenerateFromPassword(secretPass, 12)
-	if err != nil {
-		t.Error(err)
-	}
-	secret = crypto.Sha256(secret)
-
-	ciphertext := EncryptSymmetric(plaintext, secret)
-	plaintext2, err := DecryptSymmetric(ciphertext, secret)
-
-	require.NoError(t, err, "%+v", err)
-	assert.Equal(t, plaintext, plaintext2)
-}