diff --git a/src/zen_random.c b/src/zen_random.c
index 134efd2..1774573 100644
--- a/src/zen_random.c
+++ b/src/zen_random.c
@@ -68,7 +68,7 @@ void* rng_alloc() {
 		return NULL; }
 
 	// random seed provided externally 
-	if(Z->random_seed[0]) {
+	if(Z->random_external) {
 		act(Z->lua,"Random seed is external, deterministic execution");
 #ifndef ARCH_CORTEX
 	} else {
diff --git a/src/zenroom.c b/src/zenroom.c
index 1cf849f..238071d 100644
--- a/src/zenroom.c
+++ b/src/zenroom.c
@@ -161,13 +161,12 @@ zenroom_t *zen_init(const char *conf, char *keys, char *data) {
 	Z->userdata = NULL;
 	Z->errorlevel = get_debug();
 	Z->random_generator = NULL;
-	Z->random_seed[0] = 0x0; // flag for external rngseed
+	Z->random_external = 0;
 
 	// use RNGseed from configuration if present (deterministic mode)
 	if(zconf_rngseed[0] != 0x0) {
-		// short p = 0;
-		// if(zconf_rngseed[0] == '0' && zconf_rngseed[1] == 'x') p += 2;
-		// hex2buf(Z->random_seed, &zconf_rngseed[p]);
+		Z->random_external = 1;
+		memset(Z->random_seed, 0x0, 256);
 		hex2buf(Z->random_seed, zconf_rngseed);
 	}
 	// initialize the random generator
diff --git a/src/zenroom.h b/src/zenroom.h
index 911c8a2..5c4b683 100644
--- a/src/zenroom.h
+++ b/src/zenroom.h
@@ -70,6 +70,7 @@ typedef struct {
 
 	void *random_generator; // cast to RNG
 	char random_seed[RANDOM_SEED_LEN];
+	int random_external; // signal when rngseed is external
 
 	int errorlevel;
 	void *userdata; // anything passed at init (reserved for caller)
diff --git a/test/zencode_dp3t/run.sh b/test/zencode_dp3t/run.sh
index 31203dc..9613b7e 100755
--- a/test/zencode_dp3t/run.sh
+++ b/test/zencode_dp3t/run.sh
@@ -2,6 +2,8 @@
 
 # https://github.com/DP-3T/documents
 
+RNGSEED=hex:00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+
 ####################
 # common script init
 if ! test -r ../utils.sh; then
@@ -46,8 +48,8 @@ Then print the 'ephemeral ids'
 EOF
 
 
-# now generate a test with 40.000 infected SK
-cat <<EOF | $Z -z > SK_infected_40k.json
+# now generate a test with 20.000 infected SK
+cat <<EOF | $Z -z > SK_infected_20k.json
 rule check version 1.0.0
 rule input encoding hex
 rule output encoding hex
@@ -58,7 +60,7 @@ Then print the 'list of infected'
 EOF
 
 # extract a few random infected ephemeral ids to simulate proximity
-cat <<EOF | $Z -z -a SK_infected_40k.json | tee EphID_infected.json
+cat <<EOF | $Z -z -a SK_infected_20k.json | tee EphID_infected.json
 scenario 'dp3t'
 rule check version 1.0.0
 rule input encoding hex
@@ -74,7 +76,7 @@ Then print the 'ephemeral ids'
 EOF
 
 # given a list of infected and a list of ephemeral ids 
-cat <<EOF | tee dp3t_check.zen | $Z -z -a SK_infected_40k.json -k EphID_infected.json
+cat <<EOF | tee dp3t_check.zen | $Z -z -a SK_infected_20k.json -k EphID_infected.json
 scenario 'dp3t'
 rule check version 1.0.0
 rule input encoding hex
@@ -88,7 +90,7 @@ Then print the 'proximity tracing'
 EOF
 
 # given a list of infected and a list of ephemeral ids 
-# cat <<EOF | $Z -c memmanager=sys -z -a $D/SK_infected_40k.json -k $D/EphID_2.json
+# cat <<EOF | $Z -c memmanager=sys -z -a $D/SK_infected_20k.json -k $D/EphID_2.json
 # scenario 'dp3t'
 # rule check version 1.0.0
 # rule input encoding hex