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package cryptocore
import (
"crypto/sha256"
"log"
"golang.org/x/crypto/hkdf"
)
const (
// "info" data that HKDF mixes into the generated key to make it unique.
// For convenience, we use a readable string.
hkdfInfoEMENames = "EME filename encryption"
hkdfInfoGCMContent = "AES-GCM file content encryption"
hkdfInfoSIVContent = "AES-SIV file content encryption"
)
// hkdfDerive derives "outLen" bytes from "masterkey" and "info" using
// HKDF-SHA256 (RFC 5869).
// It returns the derived bytes or panics.
func hkdfDerive(masterkey []byte, info string, outLen int) (out []byte) {
h := hkdf.New(sha256.New, masterkey, nil, []byte(info))
out = make([]byte, outLen)
n, err := h.Read(out)
if n != outLen || err != nil {
log.Panicf("hkdfDerive: hkdf read failed, got %d bytes, error: %v", n, err)
}
return out
}
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