githaven/vendor/github.com/ProtonMail/go-crypto/openpgp/packet/aead_config.go

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// Copyright (C) 2019 ProtonTech AG
package packet
import "math/bits"
// AEADConfig collects a number of AEAD parameters along with sensible defaults.
// A nil AEADConfig is valid and results in all default values.
type AEADConfig struct {
// The AEAD mode of operation.
DefaultMode AEADMode
// Amount of octets in each chunk of data
ChunkSize uint64
}
// Mode returns the AEAD mode of operation.
func (conf *AEADConfig) Mode() AEADMode {
if conf == nil || conf.DefaultMode == 0 {
return AEADModeEAX
}
mode := conf.DefaultMode
if mode != AEADModeEAX && mode != AEADModeOCB &&
mode != AEADModeExperimentalGCM {
panic("AEAD mode unsupported")
}
return mode
}
// ChunkSizeByte returns the byte indicating the chunk size. The effective
// chunk size is computed with the formula uint64(1) << (chunkSizeByte + 6)
func (conf *AEADConfig) ChunkSizeByte() byte {
if conf == nil || conf.ChunkSize == 0 {
return 12 // 1 << (12 + 6) == 262144 bytes
}
chunkSize := conf.ChunkSize
exponent := bits.Len64(chunkSize) - 1
switch {
case exponent < 6:
exponent = 6
case exponent > 27:
exponent = 27
}
return byte(exponent - 6)
}
// decodeAEADChunkSize returns the effective chunk size. In 32-bit systems, the
// maximum returned value is 1 << 30.
func decodeAEADChunkSize(c byte) int {
size := uint64(1 << (c + 6))
if size != uint64(int(size)) {
return 1 << 30
}
return int(size)
}