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60 lines
1.5 KiB
Go
60 lines
1.5 KiB
Go
// (C) Copyright 2012, Jeramey Crawford <jeramey@antihe.ro>. All
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// rights reserved. Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package common
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const (
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alphabet = "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
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)
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// Base64_24Bit is a variant of Base64 encoding, commonly used with password
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// hashing algorithms to encode the result of their checksum output.
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//
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// The algorithm operates on up to 3 bytes at a time, encoding the following
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// 6-bit sequences into up to 4 hash64 ASCII bytes.
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//
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// 1. Bottom 6 bits of the first byte
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// 2. Top 2 bits of the first byte, and bottom 4 bits of the second byte.
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// 3. Top 4 bits of the second byte, and bottom 2 bits of the third byte.
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// 4. Top 6 bits of the third byte.
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//
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// This encoding method does not emit padding bytes as Base64 does.
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func Base64_24Bit(src []byte) []byte {
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if len(src) == 0 {
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return []byte{} // TODO: return nil
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}
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dstlen := (len(src)*8 + 5) / 6
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dst := make([]byte, dstlen)
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di, si := 0, 0
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n := len(src) / 3 * 3
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for si < n {
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val := uint(src[si+2])<<16 | uint(src[si+1])<<8 | uint(src[si])
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dst[di+0] = alphabet[val&0x3f]
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dst[di+1] = alphabet[val>>6&0x3f]
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dst[di+2] = alphabet[val>>12&0x3f]
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dst[di+3] = alphabet[val>>18]
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di += 4
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si += 3
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}
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rem := len(src) - si
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if rem == 0 {
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return dst
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}
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val := uint(src[si+0])
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if rem == 2 {
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val |= uint(src[si+1]) << 8
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}
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dst[di+0] = alphabet[val&0x3f]
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dst[di+1] = alphabet[val>>6&0x3f]
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if rem == 2 {
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dst[di+2] = alphabet[val>>12]
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}
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return dst
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}
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