Commit 9c0cf214 authored by Bernd Edlinger's avatar Bernd Edlinger
Browse files

Modify the RSA_private_decrypt functions to check the padding in 


constant time with a memory access pattern that does not depend
on secret information.

[extended tests]

Reviewed-by: default avatarPaul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/8543)
parent 94dc53a3

crypto/rsa/rsa_oaep.c

+16 −16
Original line number Diff line number Diff line
@@ -234,25 +234,25 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen, 
    good &= constant_time_ge(tlen, mlen);



    /*

     * Even though we can't fake result's length, we can pretend copying

     * |tlen| bytes where |mlen| bytes would be real. Last |tlen| of |dblen|

     * bytes are viewed as circular buffer with start at |tlen|-|mlen'|,

     * where |mlen'| is "saturated" |mlen| value. Deducing information

     * about failure or |mlen| would take attacker's ability to observe

     * memory access pattern with byte granularity *as it occurs*. It

     * should be noted that failure is indistinguishable from normal

     * operation if |tlen| is fixed by protocol.

     * Move the result in-place by |dblen|-|mdlen|-1-|mlen| bytes to the left.

     * Then if |good| move |mlen| bytes from |db|+|mdlen|+1 to |to|.

     * Otherwise leave |to| unchanged.

     * Copy the memory back in a way that does not reveal the size of

     * the data being copied via a timing side channel. This requires copying

     * parts of the buffer multiple times based on the bits set in the real

     * length. Clear bits do a non-copy with identical access pattern.

     * The loop below has overall complexity of O(N*log(N)).

     */

    tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen),

                                    dblen - mdlen - 1, tlen);

    msg_index = constant_time_select_int(good, msg_index, dblen - tlen);

    mlen = dblen - msg_index;

    for (mask = good, i = 0; i < tlen; i++) {

        unsigned int equals = constant_time_eq(msg_index, dblen);



        msg_index -= tlen & equals;  /* rewind at EOF */

        mask &= ~equals;  /* mask = 0 at EOF */

        to[i] = constant_time_select_8(mask, db[msg_index++], to[i]);

    for (msg_index = 1; msg_index < dblen - mdlen - 1; msg_index <<= 1) {

        mask = ~constant_time_eq(msg_index & (dblen - mdlen - 1 - mlen), 0);

        for (i = mdlen + 1; i < dblen - msg_index; i++)

            db[i] = constant_time_select_8(mask, db[i + msg_index], db[i]);

    }

    for (i = 0; i < tlen; i++) {

        mask = good & constant_time_lt(i, mlen);

        to[i] = constant_time_select_8(mask, db[i + mdlen + 1], to[i]);

    }



    /*

crypto/rsa/rsa_pk1.c

+16 −16
Original line number Diff line number Diff line
@@ -226,25 +226,25 @@ int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen, 
    good &= constant_time_ge(tlen, mlen);



    /*

     * Even though we can't fake result's length, we can pretend copying

     * |tlen| bytes where |mlen| bytes would be real. Last |tlen| of |num|

     * bytes are viewed as circular buffer with start at |tlen|-|mlen'|,

     * where |mlen'| is "saturated" |mlen| value. Deducing information

     * about failure or |mlen| would take attacker's ability to observe

     * memory access pattern with byte granularity *as it occurs*. It

     * should be noted that failure is indistinguishable from normal

     * operation if |tlen| is fixed by protocol.

     * Move the result in-place by |num|-11-|mlen| bytes to the left.

     * Then if |good| move |mlen| bytes from |em|+11 to |to|.

     * Otherwise leave |to| unchanged.

     * Copy the memory back in a way that does not reveal the size of

     * the data being copied via a timing side channel. This requires copying

     * parts of the buffer multiple times based on the bits set in the real

     * length. Clear bits do a non-copy with identical access pattern.

     * The loop below has overall complexity of O(N*log(N)).

     */

    tlen = constant_time_select_int(constant_time_lt(num - 11, tlen),

                                    num - 11, tlen);

    msg_index = constant_time_select_int(good, msg_index, num - tlen);

    mlen = num - msg_index;

    for (mask = good, i = 0; i < tlen; i++) {

        unsigned int equals = constant_time_eq(msg_index, num);



        msg_index -= tlen & equals;  /* rewind at EOF */

        mask &= ~equals;  /* mask = 0 at EOF */

        to[i] = constant_time_select_8(mask, em[msg_index++], to[i]);

    for (msg_index = 1; msg_index < num - 11; msg_index <<= 1) {

        mask = ~constant_time_eq(msg_index & (num - 11 - mlen), 0);

        for (i = 11; i < num - msg_index; i++)

            em[i] = constant_time_select_8(mask, em[i + msg_index], em[i]);

    }

    for (i = 0; i < tlen; i++) {

        mask = good & constant_time_lt(i, mlen);

        to[i] = constant_time_select_8(mask, em[i + 11], to[i]);

    }



    OPENSSL_clear_free(em, num);

crypto/rsa/rsa_ssl.c

+16 −16
Original line number Diff line number Diff line
@@ -141,25 +141,25 @@ int RSA_padding_check_SSLv23(unsigned char *to, int tlen, 
    err = constant_time_select_int(mask | good, err, RSA_R_DATA_TOO_LARGE);



    /*

     * Even though we can't fake result's length, we can pretend copying

     * |tlen| bytes where |mlen| bytes would be real. Last |tlen| of |num|

     * bytes are viewed as circular buffer with start at |tlen|-|mlen'|,

     * where |mlen'| is "saturated" |mlen| value. Deducing information

     * about failure or |mlen| would take attacker's ability to observe

     * memory access pattern with byte granularity *as it occurs*. It

     * should be noted that failure is indistinguishable from normal

     * operation if |tlen| is fixed by protocol.

     * Move the result in-place by |num|-11-|mlen| bytes to the left.

     * Then if |good| move |mlen| bytes from |em|+11 to |to|.

     * Otherwise leave |to| unchanged.

     * Copy the memory back in a way that does not reveal the size of

     * the data being copied via a timing side channel. This requires copying

     * parts of the buffer multiple times based on the bits set in the real

     * length. Clear bits do a non-copy with identical access pattern.

     * The loop below has overall complexity of O(N*log(N)).

     */

    tlen = constant_time_select_int(constant_time_lt(num - 11, tlen),

                                    num - 11, tlen);

    msg_index = constant_time_select_int(good, msg_index, num - tlen);

    mlen = num - msg_index;

    for (mask = good, i = 0; i < tlen; i++) {

        unsigned int equals = constant_time_eq(msg_index, num);



        msg_index -= tlen & equals;  /* rewind at EOF */

        mask &= ~equals;  /* mask = 0 at EOF */

        to[i] = constant_time_select_8(mask, em[msg_index++], to[i]);

    for (msg_index = 1; msg_index < num - 11; msg_index <<= 1) {

        mask = ~constant_time_eq(msg_index & (num - 11 - mlen), 0);

        for (i = 11; i < num - msg_index; i++)

            em[i] = constant_time_select_8(mask, em[i + msg_index], em[i]);

    }

    for (i = 0; i < tlen; i++) {

        mask = good & constant_time_lt(i, mlen);

        to[i] = constant_time_select_8(mask, em[i + 11], to[i]);

    }



    OPENSSL_clear_free(em, num);