make RSA blinding thread-safe

diff --git a/CHANGES b/CHANGES
index e6a179fa52837b021edade4b556f40cb540abb07..77da6273c440c033692f9f885abd706e16448ce9 100644 (file)
--- a/CHANGES
+++ b/CHANGES
@@ -483,12 +483,17 @@
      to avoid a timing attack. Applications that don't want it can call
      RSA_blinding_off() or use the new flag RSA_FLAG_NO_BLINDING.
      They would be ill-advised to do so in most cases.
-     [Ben Laurie, Steve Henson, Geoff Thorpe]
+     [Ben Laurie, Steve Henson, Geoff Thorpe, Bodo Moeller]
 
   *) Change RSA blinding code so that it works when the PRNG is not
      seeded (in this case, the secret RSA exponent is abused as
      an unpredictable seed -- if it is not unpredictable, there
-     is no point in blinding anyway).
+     is no point in blinding anyway).  Make RSA blinding thread-safe
+     by remembering the creator's thread ID in rsa->blinding and
+     having all other threads use local one-time blinding factors
+     (this requires more computation than sharing rsa->blinding, but
+     avoids excessive locking; and if an RSA object is not shared
+     between threads, blinding will still be very fast).
      [Bodo Moeller]
 
 yet to be integrated into this CVS branch:

diff --git a/crypto/bn/bn.h b/crypto/bn/bn.h
index 58263baf9a56f0d0879dab6082f1080fa5138c09..d7a5fce6ea426c2dc22e866982da7e8e9824b512 100644 (file)
--- a/crypto/bn/bn.h
+++ b/crypto/bn/bn.h
@@ -261,6 +261,8 @@ typedef struct bn_blinding_st
        BIGNUM *A;
        BIGNUM *Ai;
        BIGNUM *mod; /* just a reference */
+       unsigned long thread_id; /* added in OpenSSL 0.9.6j and 0.9.7b;
+                                 * used only by crypto/rsa/rsa_eay.c, rsa_lib.c */
        } BN_BLINDING;
 
 /* Used for montgomery multiplication */

diff --git a/crypto/rsa/rsa_eay.c b/crypto/rsa/rsa_eay.c
index 6bc6ef391344a1c88f886a2e42ab9e0309f150d1..ad6ccf634d01f28cb5eb3b569a3ea94c612434fa 100644 (file)
--- a/crypto/rsa/rsa_eay.c
+++ b/crypto/rsa/rsa_eay.c
@@ -230,6 +230,40 @@ static int rsa_eay_blinding(RSA *rsa, BN_CTX *ctx)
                        err_instr \
        } while(0)
 
+static BN_BLINDING *setup_blinding(RSA *rsa, BN_CTX *ctx)
+       {
+       BIGNUM *A, *Ai;
+       BN_BLINDING *ret = NULL;
+
+       /* added in OpenSSL 0.9.6j and 0.9.7b */
+
+       /* NB: similar code appears in RSA_blinding_on (rsa_lib.c);
+        * this should be placed in a new function of its own, but for reasons
+        * of binary compatibility can't */
+
+       BN_CTX_start(ctx);
+       A = BN_CTX_get(ctx);
+       if ((RAND_status() == 0) && rsa->d != NULL && rsa->d->d != NULL)
+               {
+               /* if PRNG is not properly seeded, resort to secret exponent as unpredictable seed */
+               RAND_add(rsa->d->d, rsa->d->dmax * sizeof rsa->d->d[0], 0);
+               if (!BN_pseudo_rand_range(A,rsa->n)) goto err;
+               }
+       else
+               {
+               if (!BN_rand_range(A,rsa->n)) goto err;
+               }
+       if ((Ai=BN_mod_inverse(NULL,A,rsa->n,ctx)) == NULL) goto err;
+
+       if (!rsa->meth->bn_mod_exp(A,A,rsa->e,rsa->n,ctx,rsa->_method_mod_n))
+               goto err;
+       ret = BN_BLINDING_new(A,Ai,rsa->n);
+       BN_free(Ai);
+err:
+       BN_CTX_end(ctx);
+       return ret;
+       }
+
 /* signing */
 static int RSA_eay_private_encrypt(int flen, const unsigned char *from,
             unsigned char *to, RSA *rsa, int padding)
@@ -238,6 +272,8 @@ static int RSA_eay_private_encrypt(int flen, const unsigned char *from,
        int i,j,k,num=0,r= -1;
        unsigned char *buf=NULL;
        BN_CTX *ctx=NULL;
+       int local_blinding = 0;
+       BN_BLINDING *blinding = NULL;
 
        BN_init(&f);
        BN_init(&ret);
@@ -275,9 +311,38 @@ static int RSA_eay_private_encrypt(int flen, const unsigned char *from,
                }
 
        BLINDING_HELPER(rsa, ctx, goto err;);
-
+       blinding = rsa->blinding;
+       
+       /* Now unless blinding is disabled, 'blinding' is non-NULL.
+        * But the BN_BLINDING object may be owned by some other thread
+        * (we don't want to keep it constant and we don't want to use
+        * lots of locking to avoid race conditions, so only a single
+        * thread can use it; other threads have to use local blinding
+        * factors) */
        if (!(rsa->flags & RSA_FLAG_NO_BLINDING))
-               if (!BN_BLINDING_convert(&f,rsa->blinding,ctx)) goto err;
+               {
+               if (blinding == NULL)
+                       {
+                       RSAerr(RSA_F_RSA_EAY_PRIVATE_ENCRYPT, ERR_R_INTERNAL_ERROR);
+                       goto err;
+                       }
+               }
+       
+       if (blinding != NULL)
+               {
+               if (blinding->thread_id != CRYPTO_thread_id())
+                       {
+                       /* we need a local one-time blinding factor */
+
+                       blinding = setup_blinding(rsa, ctx);
+                       if (blinding == NULL)
+                               goto err;
+                       local_blinding = 1;
+                       }
+               }
+
+       if (blinding)
+               if (!BN_BLINDING_convert(&f, blinding, ctx)) goto err;
 
        if ( (rsa->flags & RSA_FLAG_EXT_PKEY) ||
                ((rsa->p != NULL) &&
@@ -293,8 +358,8 @@ static int RSA_eay_private_encrypt(int flen, const unsigned char *from,
                                rsa->_method_mod_n)) goto err;
                }
 
-       if (!(rsa->flags & RSA_FLAG_NO_BLINDING))
-               if (!BN_BLINDING_invert(&ret,rsa->blinding,ctx)) goto err;
+       if (blinding)
+               if (!BN_BLINDING_invert(&ret, blinding, ctx)) goto err;
 
        /* put in leading 0 bytes if the number is less than the
         * length of the modulus */
@@ -308,6 +373,8 @@ err:
        if (ctx != NULL) BN_CTX_free(ctx);
        BN_clear_free(&ret);
        BN_clear_free(&f);
+       if (local_blinding)
+               BN_BLINDING_free(blinding);
        if (buf != NULL)
                {
                OPENSSL_cleanse(buf,num);
@@ -324,6 +391,8 @@ static int RSA_eay_private_decrypt(int flen, const unsigned char *from,
        unsigned char *p;
        unsigned char *buf=NULL;
        BN_CTX *ctx=NULL;
+       int local_blinding = 0;
+       BN_BLINDING *blinding = NULL;
 
        BN_init(&f);
        BN_init(&ret);
@@ -356,9 +425,38 @@ static int RSA_eay_private_decrypt(int flen, const unsigned char *from,
                }
 
        BLINDING_HELPER(rsa, ctx, goto err;);
-
+       blinding = rsa->blinding;
+       
+       /* Now unless blinding is disabled, 'blinding' is non-NULL.
+        * But the BN_BLINDING object may be owned by some other thread
+        * (we don't want to keep it constant and we don't want to use
+        * lots of locking to avoid race conditions, so only a single
+        * thread can use it; other threads have to use local blinding
+        * factors) */
        if (!(rsa->flags & RSA_FLAG_NO_BLINDING))
-               if (!BN_BLINDING_convert(&f,rsa->blinding,ctx)) goto err;
+               {
+               if (blinding == NULL)
+                       {
+                       RSAerr(RSA_F_RSA_EAY_PRIVATE_DECRYPT, ERR_R_INTERNAL_ERROR);
+                       goto err;
+                       }
+               }
+       
+       if (blinding != NULL)
+               {
+               if (blinding->thread_id != CRYPTO_thread_id())
+                       {
+                       /* we need a local one-time blinding factor */
+
+                       blinding = setup_blinding(rsa, ctx);
+                       if (blinding == NULL)
+                               goto err;
+                       local_blinding = 1;
+                       }
+               }
+
+       if (blinding)
+               if (!BN_BLINDING_convert(&f, blinding, ctx)) goto err;
 
        /* do the decrypt */
        if ( (rsa->flags & RSA_FLAG_EXT_PKEY) ||
@@ -376,8 +474,8 @@ static int RSA_eay_private_decrypt(int flen, const unsigned char *from,
                        goto err;
                }
 
-       if (!(rsa->flags & RSA_FLAG_NO_BLINDING))
-               if (!BN_BLINDING_invert(&ret,rsa->blinding,ctx)) goto err;
+       if (blinding)
+               if (!BN_BLINDING_invert(&ret, blinding, ctx)) goto err;
 
        p=buf;
        j=BN_bn2bin(&ret,p); /* j is only used with no-padding mode */

diff --git a/crypto/rsa/rsa_lib.c b/crypto/rsa/rsa_lib.c
index 33ca8330c9939640953a1d258a4f9ebabbc52478..3ebde4fd9326946f96125a9a0abe9a78c3c6b5af 100644 (file)
--- a/crypto/rsa/rsa_lib.c
+++ b/crypto/rsa/rsa_lib.c
@@ -329,6 +329,10 @@ int RSA_blinding_on(RSA *rsa, BN_CTX *p_ctx)
        if (rsa->blinding != NULL)
                BN_BLINDING_free(rsa->blinding);
 
+       /* NB: similar code appears in setup_blinding (rsa_eay.c);
+        * this should be placed in a new function of its own, but for reasons
+        * of binary compatibility can't */
+
        BN_CTX_start(ctx);
        A = BN_CTX_get(ctx);
        if ((RAND_status() == 0) && rsa->d != NULL && rsa->d->d != NULL)
@@ -344,8 +348,11 @@ int RSA_blinding_on(RSA *rsa, BN_CTX *p_ctx)
        if ((Ai=BN_mod_inverse(NULL,A,rsa->n,ctx)) == NULL) goto err;
 
        if (!rsa->meth->bn_mod_exp(A,A,rsa->e,rsa->n,ctx,rsa->_method_mod_n))
-           goto err;
-       rsa->blinding=BN_BLINDING_new(A,Ai,rsa->n);
+               goto err;
+       if ((rsa->blinding=BN_BLINDING_new(A,Ai,rsa->n)) == NULL) goto err;
+       /* to make things thread-safe without excessive locking,
+        * rsa->blinding will be used just by the current thread: */
+       rsa->blinding->thread_id = CRYPTO_thread_id();
        rsa->flags |= RSA_FLAG_BLINDING;
        rsa->flags &= ~RSA_FLAG_NO_BLINDING;
        BN_free(Ai);