From 32da174d1e7da3366ff8165c20cf7d063e5c40b0 Mon Sep 17 00:00:00 2001
From: rsiddharth <s@ricketyspace.net>
Date: Sun, 22 Nov 2020 12:09:33 -0500
Subject: lib: aes: add AESInvCipher

---
 lib/aes.go | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

(limited to 'lib/aes.go')

diff --git a/lib/aes.go b/lib/aes.go
index 476b366..ebad334 100644
--- a/lib/aes.go
+++ b/lib/aes.go
@@ -3,6 +3,40 @@
 
 package lib
 
+func AESInvCipher(in, ky []byte) []byte {
+	nb := 4
+	nr := 10
+
+	// Generate key schedule from key.
+	ks := KeyExpansion(ky)
+
+	// Make state from input and do first round key
+	// transformation.
+	state := MkState(in)
+	state = AddRoundKey(state, ks[(nr*nb):((nr+1)*nb)])
+
+	for round := nr - 1; round >= 1; round-- {
+		state = InvShiftRows(state)
+		state = InvSubBytes(state)
+		state = AddRoundKey(state, ks[(round*nb):((round+1)*nb)])
+		state = InvMixColumns(state)
+	}
+	state = InvShiftRows(state)
+	state = InvSubBytes(state)
+	state = AddRoundKey(state, ks[0:nb])
+
+	// Make output.
+	output := make([]byte, 4*nb)
+	i := 0
+	for c := 0; c < nb; c++ {
+		for r := 0; r < 4; r++ {
+			output[i] = state[r][c]
+			i++
+		}
+	}
+	return output
+}
+
 func InvMixColumns(state [][]byte) [][]byte {
 
 	// Initialize new state.
-- 
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