85 lines
1.9 KiB
V
85 lines
1.9 KiB
V
// The source code refers to the go standard library, which will be combined with AES in the future.
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// Use of this source code is governed by an MIT license
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// that can be found in the LICENSE file.
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//
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// Cipher Feedback Mode (CFB).
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// See NIST SP 800-38A, pp 11-13
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module cipher
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import crypto.internal.subtle
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struct Cfb {
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mut:
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b Block
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next []u8
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out []u8
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out_used int
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decrypt bool
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}
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// new_cfb_encrypter returns a `Cfb` which encrypts with cipher feedback mode,
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// using the given Block. The iv must be the same length as the Block's block
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// size
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pub fn new_cfb_encrypter(b Block, iv []u8) Cfb {
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return new_cfb(b, iv, false)
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}
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// new_cfb_decrypter returns a `Cfb` which decrypts with cipher feedback mode,
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// using the given Block. The iv must be the same length as the Block's block
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// size
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pub fn new_cfb_decrypter(b Block, iv []u8) Cfb {
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return new_cfb(b, iv, true)
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}
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fn new_cfb(b Block, iv []u8, decrypt bool) Cfb {
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block_size := b.block_size
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if iv.len != block_size {
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panic('cipher.new_cfb: IV length must be equal block size')
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}
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mut x := Cfb{
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b: b
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out: []u8{len: b.block_size}
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next: []u8{len: b.block_size}
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out_used: block_size
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decrypt: decrypt
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}
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copy(mut x.next, iv)
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return x
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}
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pub fn (mut x Cfb) xor_key_stream(mut dst_ []u8, src_ []u8) {
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unsafe {
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mut dst := *dst_
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mut src := src_
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if dst.len < src.len {
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panic('crypto.cipher.xor_key_stream: output smaller than input')
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}
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if subtle.inexact_overlap(dst[..src.len], src) {
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panic('crypto.cipher.xor_key_stream: invalid buffer overlap')
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}
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for src.len > 0 {
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if x.out_used == x.out.len {
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x.b.encrypt(mut x.out, x.next)
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x.out_used = 0
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}
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if x.decrypt {
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copy(mut x.next[x.out_used..], src)
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}
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n := xor_bytes(mut dst, src, x.out[x.out_used..])
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if !x.decrypt {
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copy(mut x.next[x.out_used..], dst)
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}
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dst = dst[n..]
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src = src[n..]
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x.out_used += n
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}
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}
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}
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