diff --git a/programs/pkey/dh_client.c b/programs/pkey/dh_client.c
index db9283a..b3a2476 100644
--- a/programs/pkey/dh_client.c
+++ b/programs/pkey/dh_client.c
@@ -70,7 +70,7 @@
     unsigned char *p, *end;
     unsigned char buf[2048];
     unsigned char hash[20];
-    char *pers = "dh_client";
+    const char *pers = "dh_client";
 
     entropy_context entropy;
     ctr_drbg_context ctr_drbg;
@@ -92,7 +92,8 @@
 
     entropy_init( &entropy );
     if( ( ret = ctr_drbg_init( &ctr_drbg, entropy_func, &entropy,
-                               (unsigned char *) pers, strlen( pers ) ) ) != 0 )
+                               (const unsigned char *) pers,
+                               strlen( pers ) ) ) != 0 )
     {
         printf( " failed\n  ! ctr_drbg_init returned %d\n", ret );
         goto exit;
diff --git a/programs/pkey/dh_genprime.c b/programs/pkey/dh_genprime.c
index 94f1c62..5732f50 100644
--- a/programs/pkey/dh_genprime.c
+++ b/programs/pkey/dh_genprime.c
@@ -62,7 +62,7 @@
     mpi G, P, Q;
     entropy_context entropy;
     ctr_drbg_context ctr_drbg;
-    char *pers = "dh_genprime";
+    const char *pers = "dh_genprime";
     FILE *fout;
 
     ((void) argc);
@@ -83,7 +83,8 @@
 
     entropy_init( &entropy );
     if( ( ret = ctr_drbg_init( &ctr_drbg, entropy_func, &entropy,
-                               (unsigned char *) pers, strlen( pers ) ) ) != 0 )
+                               (const unsigned char *) pers,
+                               strlen( pers ) ) ) != 0 )
     {
         printf( " failed\n  ! ctr_drbg_init returned %d\n", ret );
         goto exit;
diff --git a/programs/pkey/dh_server.c b/programs/pkey/dh_server.c
index 8babef2..9ea2a78 100644
--- a/programs/pkey/dh_server.c
+++ b/programs/pkey/dh_server.c
@@ -71,7 +71,7 @@
     unsigned char buf[2048];
     unsigned char hash[20];
     unsigned char buf2[2];
-    char *pers = "dh_server";
+    const char *pers = "dh_server";
 
     entropy_context entropy;
     ctr_drbg_context ctr_drbg;
@@ -93,7 +93,8 @@
 
     entropy_init( &entropy );
     if( ( ret = ctr_drbg_init( &ctr_drbg, entropy_func, &entropy,
-                               (unsigned char *) pers, strlen( pers ) ) ) != 0 )
+                               (const unsigned char *) pers,
+                               strlen( pers ) ) ) != 0 )
     {
         printf( " failed\n  ! ctr_drbg_init returned %d\n", ret );
         goto exit;
diff --git a/programs/pkey/key_app.c b/programs/pkey/key_app.c
index ebe94a7..fc0269e 100644
--- a/programs/pkey/key_app.c
+++ b/programs/pkey/key_app.c
@@ -53,9 +53,9 @@
 struct options
 {
     int mode;                   /* the mode to run the application in   */
-    char *filename;             /* filename of the key file             */
-    char *password;             /* password for the private key         */
-    char *password_file;        /* password_file for the private key    */
+    const char *filename;       /* filename of the key file             */
+    const char *password;       /* password for the private key         */
+    const char *password_file;  /* password_file for the private key    */
     int debug_level;            /* level of debugging                   */
 } opt;
 
diff --git a/programs/pkey/key_app_writer.c b/programs/pkey/key_app_writer.c
index ab05952..d8465ca 100644
--- a/programs/pkey/key_app_writer.c
+++ b/programs/pkey/key_app_writer.c
@@ -59,10 +59,10 @@
 struct options
 {
     int mode;                   /* the mode to run the application in   */
-    char *filename;             /* filename of the key file             */
+    const char *filename;       /* filename of the key file             */
     int debug_level;            /* level of debugging                   */
     int output_mode;            /* the output mode to use               */
-    char *output_file;          /* where to store the constructed key file  */
+    const char *output_file;    /* where to store the constructed key file  */
 } opt;
 
 void my_debug( void *ctx, int level, const char *str )
@@ -74,7 +74,7 @@
     }
 }
 
-void write_public_key( rsa_context *rsa, char *output_file )
+void write_public_key( rsa_context *rsa, const char *output_file )
 {
     FILE *f;
     unsigned char output_buf[16000];
@@ -111,7 +111,7 @@
     fclose(f);
 }
 
-void write_private_key( rsa_context *rsa, char *output_file )
+void write_private_key( rsa_context *rsa, const char *output_file )
 {
     FILE *f;
     unsigned char output_buf[16000];
diff --git a/programs/pkey/rsa_encrypt.c b/programs/pkey/rsa_encrypt.c
index aa6ca0e..83dcef2 100644
--- a/programs/pkey/rsa_encrypt.c
+++ b/programs/pkey/rsa_encrypt.c
@@ -60,7 +60,7 @@
     ctr_drbg_context ctr_drbg;
     unsigned char input[1024];
     unsigned char buf[512];
-    char *pers = "rsa_encrypt";
+    const char *pers = "rsa_encrypt";
 
     ret = 1;
 
@@ -80,7 +80,8 @@
 
     entropy_init( &entropy );
     if( ( ret = ctr_drbg_init( &ctr_drbg, entropy_func, &entropy,
-                               (unsigned char *) pers, strlen( pers ) ) ) != 0 )
+                               (const unsigned char *) pers,
+                               strlen( pers ) ) ) != 0 )
     {
         printf( " failed\n  ! ctr_drbg_init returned %d\n", ret );
         goto exit;
diff --git a/programs/pkey/rsa_genkey.c b/programs/pkey/rsa_genkey.c
index 424097e..68e33e5 100644
--- a/programs/pkey/rsa_genkey.c
+++ b/programs/pkey/rsa_genkey.c
@@ -62,7 +62,7 @@
     ctr_drbg_context ctr_drbg;
     FILE *fpub  = NULL;
     FILE *fpriv = NULL;
-    char *pers = "rsa_genkey";
+    const char *pers = "rsa_genkey";
 
     ((void) argc);
     ((void) argv);
@@ -72,7 +72,8 @@
 
     entropy_init( &entropy );
     if( ( ret = ctr_drbg_init( &ctr_drbg, entropy_func, &entropy,
-                               (unsigned char *) pers, strlen( pers ) ) ) != 0 )
+                               (const unsigned char *) pers,
+                               strlen( pers ) ) ) != 0 )
     {
         printf( " failed\n  ! ctr_drbg_init returned %d\n", ret );
         goto exit;
diff --git a/programs/pkey/rsa_sign_pss.c b/programs/pkey/rsa_sign_pss.c
index ffc5de0..17e772a 100644
--- a/programs/pkey/rsa_sign_pss.c
+++ b/programs/pkey/rsa_sign_pss.c
@@ -69,7 +69,7 @@
     unsigned char hash[20];
     unsigned char buf[POLARSSL_MPI_MAX_SIZE];
     char filename[512];
-    char *pers = "rsa_sign_pss";
+    const char *pers = "rsa_sign_pss";
 
     ret = 1;
 
@@ -89,7 +89,8 @@
 
     entropy_init( &entropy );
     if( ( ret = ctr_drbg_init( &ctr_drbg, entropy_func, &entropy,
-                               (unsigned char *) pers, strlen( pers ) ) ) != 0 )
+                               (const unsigned char *) pers,
+                               strlen( pers ) ) ) != 0 )
     {
         printf( " failed\n  ! ctr_drbg_init returned %d\n", ret );
         goto exit;