forked from toolshed/abra
68 lines
1.8 KiB
Go
68 lines
1.8 KiB
Go
// Copyright (C) 2019 ProtonTech AG
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package packet
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import "math/bits"
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// CipherSuite contains a combination of Cipher and Mode
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type CipherSuite struct {
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// The cipher function
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Cipher CipherFunction
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// The AEAD mode of operation.
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Mode AEADMode
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}
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// AEADConfig collects a number of AEAD parameters along with sensible defaults.
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// A nil AEADConfig is valid and results in all default values.
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type AEADConfig struct {
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// The AEAD mode of operation.
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DefaultMode AEADMode
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// Amount of octets in each chunk of data
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ChunkSize uint64
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}
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// Mode returns the AEAD mode of operation.
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func (conf *AEADConfig) Mode() AEADMode {
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// If no preference is specified, OCB is used (which is mandatory to implement).
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if conf == nil || conf.DefaultMode == 0 {
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return AEADModeOCB
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}
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mode := conf.DefaultMode
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if mode != AEADModeEAX && mode != AEADModeOCB && mode != AEADModeGCM {
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panic("AEAD mode unsupported")
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}
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return mode
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}
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// ChunkSizeByte returns the byte indicating the chunk size. The effective
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// chunk size is computed with the formula uint64(1) << (chunkSizeByte + 6)
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// limit chunkSizeByte to 16 which equals to 2^22 = 4 MiB
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// https://www.ietf.org/archive/id/draft-ietf-openpgp-crypto-refresh-07.html#section-5.13.2
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func (conf *AEADConfig) ChunkSizeByte() byte {
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if conf == nil || conf.ChunkSize == 0 {
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return 12 // 1 << (12 + 6) == 262144 bytes
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}
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chunkSize := conf.ChunkSize
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exponent := bits.Len64(chunkSize) - 1
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switch {
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case exponent < 6:
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exponent = 6
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case exponent > 22:
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exponent = 22
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}
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return byte(exponent - 6)
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}
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// decodeAEADChunkSize returns the effective chunk size. In 32-bit systems, the
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// maximum returned value is 1 << 30.
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func decodeAEADChunkSize(c byte) int {
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size := uint64(1 << (c + 6))
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if size != uint64(int(size)) {
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return 1 << 30
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}
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return int(size)
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}
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