55 lines
1.7 KiB
Go
55 lines
1.7 KiB
Go
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package symm
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import (
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"crypto/cipher"
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"errors"
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)
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var (
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ErrSegmentNotFullBlocks = errors.New("ciphertext segment is not a full block size")
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)
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func decryptECBBlocks(block cipher.Block, src []byte) ([]byte, error) {
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if len(src) == 0 {
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return []byte{}, nil
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}
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if len(src)%block.BlockSize() != 0 {
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return nil, ErrSegmentNotFullBlocks
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}
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out := make([]byte, len(src))
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ecbDecryptBlocks(block, out, src)
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return out, nil
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}
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// decryptCBCFromSecondBlock decrypts a CBC ciphertext segment that starts from the second block (or later).
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// prevCipherBlock must be the previous ciphertext block (C[i-1]); for i=1 this is the original IV.
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func decryptCBCFromSecondBlock(block cipher.Block, src, prevCipherBlock []byte) ([]byte, error) {
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if len(src) == 0 {
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return []byte{}, nil
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}
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if len(prevCipherBlock) != block.BlockSize() {
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return nil, errors.New("prev cipher block length must match block size")
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}
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if len(src)%block.BlockSize() != 0 {
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return nil, ErrSegmentNotFullBlocks
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}
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out := make([]byte, len(src))
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cipher.NewCBCDecrypter(block, prevCipherBlock).CryptBlocks(out, src)
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return out, nil
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}
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// decryptCFBFromSecondBlock decrypts a CFB ciphertext segment that starts from the second block (or later).
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// prevCipherBlock must be the previous ciphertext block (C[i-1]); for i=1 this is the original IV.
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func decryptCFBFromSecondBlock(block cipher.Block, src, prevCipherBlock []byte) ([]byte, error) {
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if len(src) == 0 {
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return []byte{}, nil
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}
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if len(prevCipherBlock) != block.BlockSize() {
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return nil, errors.New("prev cipher block length must match block size")
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}
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stream := cipher.NewCFBDecrypter(block, prevCipherBlock)
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out := make([]byte, len(src))
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stream.XORKeyStream(out, src)
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return out, nil
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}
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