1 files changed, 29 insertions, 0 deletions

diff --git a/src/lib/libcrypto/jpake/jpake.c b/src/lib/libcrypto/jpake/jpake.c
index 086d9f47e0..8e4b633ccc 100644
--- a/src/lib/libcrypto/jpake/jpake.c
+++ b/src/lib/libcrypto/jpake/jpake.c
@@ -282,8 +282,37 @@ int JPAKE_STEP1_generate(JPAKE_STEP1 *send, JPAKE_CTX *ctx)
     return 1;
     }
 
+/* g^x is a legal value */
+static int is_legal(const BIGNUM *gx, const JPAKE_CTX *ctx)
+    {
+    BIGNUM *t;
+    int res;
+    
+    if(BN_is_negative(gx) || BN_is_zero(gx) || BN_cmp(gx, ctx->p.p) >= 0)
+        return 0;
+
+    t = BN_new();
+    BN_mod_exp(t, gx, ctx->p.q, ctx->p.p, ctx->ctx);
+    res = BN_is_one(t);
+    BN_free(t);
+
+    return res;
+    }
+
 int JPAKE_STEP1_process(JPAKE_CTX *ctx, const JPAKE_STEP1 *received)
     {
+    if(!is_legal(received->p1.gx, ctx))
+        {
+        JPAKEerr(JPAKE_F_JPAKE_STEP1_PROCESS, JPAKE_R_G_TO_THE_X3_IS_NOT_LEGAL);
+        return 0;
+        }
+
+    if(!is_legal(received->p2.gx, ctx))
+        {
+        JPAKEerr(JPAKE_F_JPAKE_STEP1_PROCESS, JPAKE_R_G_TO_THE_X4_IS_NOT_LEGAL);
+        return 0;
+        }
+
    /* verify their ZKP(xc) */
     if(!verify_zkp(&received->p1, ctx->p.g, ctx))
         {