[openssl-users] CBC ciphers + TLS 1.0 protocol does not work in OpenSSL 1.0.2d

[Jayalakshmi bhat]

Hi Matt,

s3_cbc.c uses the function constant_time_eq_8. I pulled only this
function definition from OpenSSL 1.0.1e into OpenSSL 1.0.2d. I renamed this
function as constant_time_eq_8_local and used it in s3_cbc.c instead of
constant_time_eq_8. This renaming was just to avoid multiple definitions.

OpenSSL 1.0.1e has the function constant_time_eq_8 defined as below:

*#define DUPLICATE_MSB_TO_ALL(x) ( (unsigned)( (int)(x) >>
(sizeof(int)*8-1) ) )#define DUPLICATE_MSB_TO_ALL_8(x) ((unsigned
char)(DUPLICATE_MSB_TO_ALL(x)))*

*static unsigned char constant_time_eq_8(unsigned a, unsigned b)*
* {*
* unsigned c = a ^ b;*
* c--;*
* return DUPLICATE_MSB_TO_ALL_8(c);*
* }*

OpenSSL 1.0.2d has the function constant_time_eq_8 defined as below.

static inline unsigned int constant_time_msb(unsigned int a)
{
    return 0 - (a >> (sizeof(a) * 8 - 1));
}

static inline unsigned int constant_time_is_zero(unsigned int a)
{
    return constant_time_msb(~a & (a - 1));
}

static inline unsigned int constant_time_eq(unsigned int a, unsigned int b)
{
    return constant_time_is_zero(a ^ b);
}

static inline unsigned char constant_time_eq_8(unsigned int a, unsigned int
b)
{
    return (unsigned char)(constant_time_eq(a, b));
}


Regards
Jaya

On Fri, Dec 4, 2015 at 7:04 PM, Matt Caswell <matt at openssl.org> wrote:

>
>
> On 04/12/15 11:31, Jayalakshmi bhat wrote:
> > Hi Matt,
> >
> > Thanks a lot for the response.
> >
> > Is your application a client or a server? Are both ends using
> > OpenSSL 1.0.2d? If not, what is the other end using?
> >>>Our device has both TLS client,server apps. As client, device
> communicates with radius server, LDAP server etc.As
> > server device is accessed using various web browsers.
> > Hence both the end will not be OpenSSL 1.0.2d.
> >
> > How exactly are you doing that? Which specific cipher are you seeing
> fail?
> >>> We have provided user option to select TLS protocol versions similar
> to the browsers. Depending upon the user configurations we set the protocol
> flags (SSL_OP_NO_TLSv1,SSL_OP_NO_TLSv1_1, SSL_OP_NO_TLSv1_2) in the SSL
> context using SSL_CTX_clear_options/SSL_CTX_set_options.
> >>> We have provided user option to chose ciphers as well.
> > All these are in the application space,no changes have been done and
> > they have been working good with OpenSSL 1.0.1c. Only the library is
> > upgraded to OpenSSL 1.0.2d.I have used AES256-CBC and AES128 CBC ciphers
> > and with both the ciphers issue is seen.
> >
> > Are you able to provide a packet capture?
> >>> Please find the attached traces for server mode.
> > What O/S is this on?
> >>>This is built for WinCE and Vxworks
>
> Thanks. Please could you also send the exact patch that you applied that
> resolved the issue?
>
> Matt
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