From 51cce8132d7bd21f51613a1a78ea6652ffb222f4 Mon Sep 17 00:00:00 2001 From: rsiddharth Date: Wed, 3 Mar 2021 20:14:16 -0500 Subject: lib: add AESGenCTRFunc --- lib/aes.go | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) (limited to 'lib') diff --git a/lib/aes.go b/lib/aes.go index 82ee8ed..f3fd6d9 100644 --- a/lib/aes.go +++ b/lib/aes.go @@ -3,6 +3,29 @@ package lib +// Generates counter function for AES CTR mode. +func AESGenCTRFunc(nonce uint64) func() []byte { + ctr := uint64(0) // Counter + ff := uint64(0xFF) + cf := func() []byte { + cb := make([]byte, 16) // counter block + var i, j uint + // Put nonce in the first 8 bytes in cb in little endian format + for i = 0; i < 8; i++ { + n := nonce & (ff << (i * 8)) // Reset all except the i^th byte of the nonce + cb[i] = byte(n >> (i * 8)) // Retrieve i^th byte of the nonce + } + // Put counter in the next 8 bytes in cb in little endian format + for i, j = 8, 0; i < 16; i, j = i+1, j+1 { + n := ctr & (ff << (j * 8)) // Reset all except the j^th byte of the counter + cb[i] = byte(n >> (j * 8)) // Retrieve j^th byte of the counter + } + ctr += 1 // Increment counter by 1 + return cb + } + return cf +} + func AESEncryptCTR(plain, key []byte, ctrFunc func() []byte) ([]byte, error) { if len(key) != 16 { return []byte{}, CPError{"key length != 16"} -- cgit v1.2.3