[FFmpeg-devel] libavutil: Added cbc mode to cast5.c
supraja reddy
supraja0493 at gmail.com
Thu Dec 18 11:09:52 CET 2014
Sorry for the mistake . I seem to have got cbc completely wrong.
I have made the changes . Please let me know if there is anything missing.
Supraja
On Thu, Dec 18, 2014 at 2:57 PM, Giorgio Vazzana <mywing81 at gmail.com> wrote:
>
> Hello,
>
> 2014-12-17 19:53 GMT+01:00 supraja reddy <supraja0493 at gmail.com>:
> > I hope this fixes all the issues .
>
> > From 16c8db86ebf92f68a8a750dcbe5e3598a8bd69b5 Mon Sep 17 00:00:00 2001
> > From: Supraja Meedinti <supraja0493 at gmail.com>
> > Date: Thu, 18 Dec 2014 00:17:45 +0530
> > Subject: [PATCH] libavutil: Added cbc mode to cast128
> >
> > Signed-off-by: Supraja Meedinti <supraja0493 at gmail.com>
> > ---
> > libavutil/cast5.c | 40 ++++++++++++++++++++++++++++++++++++++--
> > libavutil/cast5.h | 14 +++++++++++++-
> > 2 files changed, 51 insertions(+), 3 deletions(-)
> >
> > diff --git a/libavutil/cast5.c b/libavutil/cast5.c
> > index 14dd701..dba5b6a 100644
> > --- a/libavutil/cast5.c
> > +++ b/libavutil/cast5.c
> > @@ -416,7 +416,7 @@ static void encipher(AVCAST5* cs, uint8_t* dst,
> const uint8_t* src)
> > AV_WB32(dst + 4, l);
> > }
> >
> > -static void decipher(AVCAST5* cs, uint8_t* dst, const uint8_t* src)
> > +static void decipher(AVCAST5* cs, uint8_t* dst, const uint8_t* src,
> uint8_t *iv)
> > {
> > uint32_t f, I, r, l;
> > l = AV_RB32(src);
> > @@ -439,6 +439,11 @@ static void decipher(AVCAST5* cs, uint8_t* dst,
> const uint8_t* src)
> > F3(r, l, 3);
> > F2(l, r, 2);
> > F1(r, l, 1);
> > + if (iv) {
> > + r ^= AV_RB32(iv);
> > + l ^= AV_RB32(iv + 4);
> > + memcpy(iv, src, 8);
>
> Indentation is off.
>
> > + }
> > AV_WB32(dst, r);
> > AV_WB32(dst + 4, l);
> > }
> > @@ -468,11 +473,30 @@ av_cold int av_cast5_init(AVCAST5* cs, const
> uint8_t *key, int key_bits)
> > return 0;
> > }
> >
> > +void av_cast5_crypt2(AVCAST5* cs, uint8_t* dst, const uint8_t* src, int
> count, uint8_t *iv, int decrypt)
> > +{
> > + int i;
> > + while (count--) {
> > + if (decrypt){
>
> Missing space between ) and {.
>
> > + decipher(cs, dst, src, iv);
> > + } else {
>
> The indentation of this else branch is wrong.
>
> > + if (iv) {
> > + for (i = 0; i < 8; i++)
> > + dst[i] = src[i] ^ iv[i];
> > + encipher(cs, dst, dst);
>
> Again, you are not saving the IV for the next block here.
>
> > + } else {
> > + encipher(cs, dst, src);
> > + }
> > + }
> > + src = src + 8;
> > + dst = dst + 8;
> > + }
> > +}
> > void av_cast5_crypt(AVCAST5* cs, uint8_t* dst, const uint8_t* src, int
> count, int decrypt)
> > {
> > while (count--) {
> > if (decrypt){
> > - decipher(cs, dst, src);
> > + decipher(cs, dst, src, NULL);
> > } else {
> > encipher(cs, dst, src);
> > }
> > @@ -504,6 +528,7 @@ int main(int argc, char** argv)
> > {0xee, 0xa9, 0xd0, 0xa2, 0x49, 0xfd, 0x3b, 0xa6, 0xb3, 0x43,
> 0x6f, 0xb8, 0x9d, 0x6d, 0xca, 0x92},
> > {0xb2, 0xc9, 0x5e, 0xb0, 0x0c, 0x31, 0xad, 0x71, 0x80, 0xac,
> 0x05, 0xb8, 0xe8, 0x3d, 0x69, 0x6e}
> > };
> > + uint8_t iv[8] = {0xee, 0xa9, 0xd0, 0xa2, 0x49, 0xfd, 0x3b, 0xa6};
> > static uint8_t rpt2[2][16];
> > int i, j, err = 0;
> > static int key_bits[3] = {128, 80, 40};
> > @@ -547,6 +572,17 @@ int main(int argc, char** argv)
> > }
> > }
> > }
> > + for (j = 0; j < 3; j++) {
> > + av_cast5_init(cs, Key[j], key_bits[j]);
> > + av_cast5_crypt2(cs, temp, rpt, 1, iv, 0);
> > + av_cast5_crypt2(cs, temp, temp, 1, iv, 1);
> > + for (i =0; i < 8; i++) {
>
> Missing space after =.
>
> > + if (rpt[i] != temp[i]) {
> > + av_log(NULL, AV_LOG_ERROR, "%d %02x %02x\n", i, rpt[i],
> temp[i]);
> > + err = 1;
> > + }
> > + }
> > + }
>
> I see at least 2 problems with this for loop:
>
> 1) you need to use the same IV to encrypt and decrypt the block. It
> seems to work here because you forgot to propagate the IV correctly in
> av_cast5_crypt2, otherwise after the encryption the IV would change,
> and so you would be using a different IV for the decryption.
> 2) to correctly test CBC mode we need to work on 2 blocks at least.
>
> > av_free(cs);
> > return err;
> > }
> > diff --git a/libavutil/cast5.h b/libavutil/cast5.h
> > index 913d048..4a86743 100644
> > --- a/libavutil/cast5.h
> > +++ b/libavutil/cast5.h
> > @@ -52,7 +52,7 @@ struct AVCAST5 *av_cast5_alloc(void);
> > int av_cast5_init(struct AVCAST5 *ctx, const uint8_t *key, int
> key_bits);
> >
> > /**
> > - * Encrypt or decrypt a buffer using a previously initialized context
> > + * Encrypt or decrypt a buffer using a previously initialized context,
> ECB mode only
> > *
> > * @param ctx an AVCAST5 context
> > * @param dst destination array, can be equal to src
> > @@ -61,6 +61,18 @@ int av_cast5_init(struct AVCAST5 *ctx, const uint8_t
> *key, int key_bits);
> > * @param decrypt 0 for encryption, 1 for decryption
> > */
> > void av_cast5_crypt(struct AVCAST5 *ctx, uint8_t *dst, const uint8_t
> *src, int count, int decrypt);
> > +
> > +/**
> > + * Encrypt or decrypt a buffer using a previously initialized context
> > + *
> > + * @param ctx an AVCAST5 context
> > + * @param dst destination array, can be equal to src
> > + * @param src source array, can be equal to dst
> > + * @param count number of 8 byte blocks
> > + * @param iv initialization vector for cbc mode, NULL for ecb mode
> > + * @param decrypt 0 for encryption, 1 for decryption
> > + */
> > +void av_cast5_crypt2(struct AVCAST5 *ctx, uint8_t *dst, const uint8_t
> *src, int count, uint8_t *iv, int decrypt);
> > /**
> > * @}
> > */
> > --
> > 1.8.3.2
> >
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>
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