commit c762521e7389dbe2f17d40217890e4307b7a1d18
author Janos Follath <janos.follath@arm.com> Wed Dec 27 10:33:00 2023 +0000
committer Janos Follath <janos.follath@arm.com> Wed Dec 27 10:33:00 2023 +0000
tree b2a7f7ff4ade1c069e2f3134d5a19312d7d81e5b
parent dad6d6666141cd9aee7c18f4cda403e738d1f5fd

RSA: remove unneeded temporaries

Signed-off-by: Janos Follath <janos.follath@arm.com>

library/rsa.c

diff --git a/library/rsa.c b/library/rsa.c
index 803759b..1357e1b 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -1068,18 +1068,9 @@
     /* Temporaries holding the blinded exponents for
      * the mod p resp. mod q computation (if used). */
     mbedtls_mpi DP_blind, DQ_blind;
-
-    /* Pointers to actual exponents to be used - either the unblinded
-     * or the blinded ones, depending on the presence of a PRNG. */
-    mbedtls_mpi *DP = &ctx->DP;
-    mbedtls_mpi *DQ = &ctx->DQ;
 #else
     /* Temporary holding the blinded exponent (if used). */
     mbedtls_mpi D_blind;
-
-    /* Pointer to actual exponent to be used - either the unblinded
-     * or the blinded one, depending on the presence of a PRNG. */
-    mbedtls_mpi *D = &ctx->D;
 #endif /* MBEDTLS_RSA_NO_CRT */
 
     /* Temporaries holding the initial input and the double
@@ -1155,8 +1146,6 @@
     MBEDTLS_MPI_CHK(mbedtls_mpi_mul_mpi(&D_blind, &P1, &Q1));
     MBEDTLS_MPI_CHK(mbedtls_mpi_mul_mpi(&D_blind, &D_blind, &R));
     MBEDTLS_MPI_CHK(mbedtls_mpi_add_mpi(&D_blind, &D_blind, &ctx->D));
-
-    D = &D_blind;
 #else
     /*
      * DP_blind = ( P - 1 ) * R + DP
@@ -1167,8 +1156,6 @@
     MBEDTLS_MPI_CHK(mbedtls_mpi_add_mpi(&DP_blind, &DP_blind,
                                         &ctx->DP));
 
-    DP = &DP_blind;
-
     /*
      * DQ_blind = ( Q - 1 ) * R + DQ
      */
@@ -1177,12 +1164,10 @@
     MBEDTLS_MPI_CHK(mbedtls_mpi_mul_mpi(&DQ_blind, &Q1, &R));
     MBEDTLS_MPI_CHK(mbedtls_mpi_add_mpi(&DQ_blind, &DQ_blind,
                                         &ctx->DQ));
-
-    DQ = &DQ_blind;
 #endif /* MBEDTLS_RSA_NO_CRT */
 
 #if defined(MBEDTLS_RSA_NO_CRT)
-    MBEDTLS_MPI_CHK(mbedtls_mpi_exp_mod(&T, &T, D, &ctx->N, &ctx->RN));
+    MBEDTLS_MPI_CHK(mbedtls_mpi_exp_mod(&T, &T, &D_blind, &ctx->N, &ctx->RN));
 #else
     /*
      * Faster decryption using the CRT
@@ -1191,8 +1176,8 @@
      * TQ = input ^ dQ mod Q
      */
 
-    MBEDTLS_MPI_CHK(mbedtls_mpi_exp_mod(&TP, &T, DP, &ctx->P, &ctx->RP));
-    MBEDTLS_MPI_CHK(mbedtls_mpi_exp_mod(&TQ, &T, DQ, &ctx->Q, &ctx->RQ));
+    MBEDTLS_MPI_CHK(mbedtls_mpi_exp_mod(&TP, &T, &DP_blind, &ctx->P, &ctx->RP));
+    MBEDTLS_MPI_CHK(mbedtls_mpi_exp_mod(&TQ, &T, &DQ_blind, &ctx->Q, &ctx->RQ));
 
     /*
      * T = (TP - TQ) * (Q^-1 mod P) mod P