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cryptocore: derive 512-bit key for AES-SIV

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AES-SIV uses 1/2 of the key for authentication, 1/2 for
encryption, so we need a 64-byte key for AES-256. Derive
it from the master key by hashing it with SHA-512.
This commit is contained in:
Jakob Unterwurzacher 2016-10-04 00:12:29 +02:00
parent 46018785b4
commit bb52937834
1 changed files with 6 additions and 1 deletions
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7
internal/cryptocore/cryptocore.go
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@ -5,6 +5,7 @@ package cryptocore
import (
"crypto/aes"
"crypto/cipher"
"crypto/sha512"
"fmt"
"github.com/rfjakob/gocryptfs/internal/siv_aead"
@ -64,7 +65,11 @@ func New(key []byte, backend BackendTypeEnum, IVBitLen int) *CryptoCore {
case BackendGoGCM:
gcm, err = goGCMWrapper(blockCipher, IVLen)
case BackendAESSIV:
gcm = siv_aead.New(key)
// AES-SIV uses 1/2 of the key for authentication, 1/2 for
// encryption, so we need a 64-bytes key for AES-256. Derive it from
// the master key by hashing it with SHA-512.
key64 := sha512.Sum512(key)
gcm = siv_aead.New(key64[:])
default:
panic("unknown backend cipher")
}