From a052dd6532321ebb01936d1dcdb99481f741ad6a Mon Sep 17 00:00:00 2001
From: Ben Laurie <ben@openssl.org>
Date: Sun, 27 Jul 2003 13:46:57 +0000
Subject: [PATCH] Add untested CFB-r mode. Will be tested soon.

---
 crypto/aes/aes.h     |  3 +++
 crypto/aes/aes_cfb.c | 57 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+)

diff --git a/crypto/aes/aes.h b/crypto/aes/aes.h
index da067f4a8f..9ba4e61a21 100644
--- a/crypto/aes/aes.h
+++ b/crypto/aes/aes.h
@@ -95,6 +95,9 @@ void AES_cbc_encrypt(const unsigned char *in, unsigned char *out,
 void AES_cfb128_encrypt(const unsigned char *in, unsigned char *out,
 	const unsigned long length, const AES_KEY *key,
 	unsigned char *ivec, int *num, const int enc);
+void AES_cfbr_encrypt_block(const unsigned char *in,unsigned char *out,
+			    const int nbits,const AES_KEY *key,
+			    unsigned char *ivec,const int enc);
 void AES_ofb128_encrypt(const unsigned char *in, unsigned char *out,
 	const unsigned long length, const AES_KEY *key,
 	unsigned char *ivec, int *num);
diff --git a/crypto/aes/aes_cfb.c b/crypto/aes/aes_cfb.c
index 9b569dda90..209a346748 100644
--- a/crypto/aes/aes_cfb.c
+++ b/crypto/aes/aes_cfb.c
@@ -155,3 +155,60 @@ void AES_cfb128_encrypt(const unsigned char *in, unsigned char *out,
 	*num=n;
 }
 
+/* This expects a single block of size nbits for both in and out. Note that
+   it corrupts any extra bits in the last byte of out */
+/* Untested, once it is working, it will be optimised */
+void AES_cfbr_encrypt_block(const unsigned char *in,unsigned char *out,
+			    const int nbits,const AES_KEY *key,
+			    unsigned char *ivec,const int enc)
+    {
+    unsigned int n;
+    unsigned char ovec[AES_BLOCK_SIZE*2];
+
+    assert(in && out && key && ivec);
+    if(enc)
+	{
+	/* construct the new IV in the second half of ovec */
+	AES_encrypt(ivec,ovec+AES_BLOCK_SIZE,key);
+	/* encrypt the input */
+	for(n=0 ; n < (nbits+7)/8 ; ++n)
+	    out[n]=in[n]^ovec[n+AES_BLOCK_SIZE];
+	/* fill in the first half of the new IV with the current IV */
+	memcpy(ovec,ivec,AES_BLOCK_SIZE);
+	/* shift ovec left most of the bits... */
+	memmove(ovec,ovec+nbits/8,AES_BLOCK_SIZE+(nbits%8 ? 1 : 0));
+	/* now the remaining bits */
+	if(nbits%8 != 0)
+	    for(n=0 ; n < AES_BLOCK_SIZE ; ++n)
+		{
+		ovec[n]<<=nbits%8;
+		ovec[n]|=ovec[n+1]>>(8-nbits%8);
+		}
+	/* finally, move it back into place */
+	memcpy(ivec,ovec,AES_BLOCK_SIZE);
+	}
+    else
+	{
+	/* construct the new IV in the first half of ovec */
+	AES_encrypt(ivec,ovec,key);
+	/* decrypt the input */
+	for(n=0 ; n < (nbits+7)/8 ; ++n)
+	    out[n]=in[n]^ovec[n];
+	/* fill in the first half of the new IV with the current IV */
+	memcpy(ovec,ivec,AES_BLOCK_SIZE);
+	/* append the ciphertext */
+	memcpy(ovec+AES_BLOCK_SIZE,in,(nbits+7)/8);
+	/* shift ovec left most of the bits... */
+	memmove(ovec,ovec+nbits/8,AES_BLOCK_SIZE+(nbits%8 ? 1 : 0));
+	/* now the remaining bits */
+	if(nbits%8 != 0)
+	    for(n=0 ; n < AES_BLOCK_SIZE ; ++n)
+		{
+		ovec[n]<<=nbits%8;
+		ovec[n]|=ovec[n+1]>>(8-nbits%8);
+		}
+	/* finally, move it back into place */
+	memcpy(ivec,ovec,AES_BLOCK_SIZE);
+	}
+    /* it is not necessary to cleanse ovec, since the IV is not secret */
+    }
-- 
2.25.1