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// Copyright (c) 2021 Tulir Asokan
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
// Package hkdfutil contains a simple wrapper for golang.org/x/crypto/hkdf that reads a specified number of bytes.
package hkdfutil
import (
"crypto/sha256"
"fmt"
"golang.org/x/crypto/hkdf"
)
func SHA256(key, salt, info []byte, length uint8) []byte {
data := make([]byte, length)
h := hkdf.New(sha256.New, key, salt, info)
n, err := h.Read(data)
if err != nil {
// Length is limited to 255 by being uint8, so these errors can't actually happen
panic(fmt.Errorf("failed to expand key: %w", err))
} else if uint8(n) != length {
panic(fmt.Errorf("didn't read enough bytes (got %d, wanted %d)", n, length))
}
return data
}
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