30 lines
860 B
Go
30 lines
860 B
Go
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package handshake
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import (
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"crypto"
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"encoding/binary"
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"golang.org/x/crypto/hkdf"
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)
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// hkdfExpandLabel HKDF expands a label.
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// Since this implementation avoids using a cryptobyte.Builder, it is about 15% faster than the
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// hkdfExpandLabel in the standard library.
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func hkdfExpandLabel(hash crypto.Hash, secret, context []byte, label string, length int) []byte {
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b := make([]byte, 3, 3+6+len(label)+1+len(context))
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binary.BigEndian.PutUint16(b, uint16(length))
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b[2] = uint8(6 + len(label))
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b = append(b, []byte("tls13 ")...)
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b = append(b, []byte(label)...)
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b = b[:3+6+len(label)+1]
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b[3+6+len(label)] = uint8(len(context))
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b = append(b, context...)
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out := make([]byte, length)
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n, err := hkdf.Expand(hash.New, secret, b).Read(out)
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if err != nil || n != length {
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panic("quic: HKDF-Expand-Label invocation failed unexpectedly")
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}
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return out
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}
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