diff --git a/extmod/modtrezorcrypto/modtrezorcrypto-aes.h b/extmod/modtrezorcrypto/modtrezorcrypto-aes.h
index e032a57416..9f56b86dff 100644
--- a/extmod/modtrezorcrypto/modtrezorcrypto-aes.h
+++ b/extmod/modtrezorcrypto/modtrezorcrypto-aes.h
@@ -90,9 +90,12 @@ STATIC mp_obj_t mod_TrezorCrypto_AES_make_new(const mp_obj_type_t *type, size_t
 STATIC mp_obj_t mod_TrezorCrypto_AES_update(mp_obj_t self, mp_obj_t data) {
     mp_buffer_info_t buf;
     mp_get_buffer_raise(data, &buf, MP_BUFFER_READ);
-    mp_obj_AES_t *o = MP_OBJ_TO_PTR(self);
     vstr_t vstr;
     vstr_init_len(&vstr, buf.len);
+    if (buf.len == 0) {
+        return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
+    }
+    mp_obj_AES_t *o = MP_OBJ_TO_PTR(self);
     switch (o->mode & AESModeMask) {
         case ECB:
             if (buf.len & (AES_BLOCK_SIZE - 1)) {
diff --git a/extmod/modtrezorcrypto/modtrezorcrypto-bip39.h b/extmod/modtrezorcrypto/modtrezorcrypto-bip39.h
index 8c6e659a80..636aa2b05e 100644
--- a/extmod/modtrezorcrypto/modtrezorcrypto-bip39.h
+++ b/extmod/modtrezorcrypto/modtrezorcrypto-bip39.h
@@ -62,7 +62,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_TrezorCrypto_Bip39_from_data_obj, mod_Trezo
 STATIC mp_obj_t mod_TrezorCrypto_Bip39_check(mp_obj_t self, mp_obj_t mnemonic) {
     mp_buffer_info_t text;
     mp_get_buffer_raise(mnemonic, &text, MP_BUFFER_READ);
-    return mnemonic_check(text.buf) ? mp_const_true : mp_const_false;
+    return (text.len > 0 && mnemonic_check(text.buf)) ? mp_const_true : mp_const_false;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_TrezorCrypto_Bip39_check_obj, mod_TrezorCrypto_Bip39_check);
 
@@ -77,7 +77,9 @@ STATIC mp_obj_t mod_TrezorCrypto_Bip39_seed(mp_obj_t self, mp_obj_t mnemonic, mp
     mp_get_buffer_raise(passphrase, &phrase, MP_BUFFER_READ);
     vstr_t vstr;
     vstr_init_len(&vstr, 64);
-    mnemonic_to_seed(mnemo.buf, phrase.buf, (uint8_t *)vstr.buf, NULL); // no callback for now
+    const char *pmnemonic = mnemo.len > 0 ? mnemo.buf : "";
+    const char *ppassphrase = phrase.len > 0 ? phrase.buf : "";
+    mnemonic_to_seed(pmnemonic, ppassphrase, (uint8_t *)vstr.buf, NULL); // no callback for now
     return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_3(mod_TrezorCrypto_Bip39_seed_obj, mod_TrezorCrypto_Bip39_seed);
diff --git a/extmod/modtrezorcrypto/modtrezorcrypto-ed25519.h b/extmod/modtrezorcrypto/modtrezorcrypto-ed25519.h
index 0a9ae59a89..b764cc1427 100644
--- a/extmod/modtrezorcrypto/modtrezorcrypto-ed25519.h
+++ b/extmod/modtrezorcrypto/modtrezorcrypto-ed25519.h
@@ -48,6 +48,9 @@ STATIC mp_obj_t mod_TrezorCrypto_Ed25519_sign(mp_obj_t self, mp_obj_t secret_key
     if (sk.len != 32) {
         nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "Invalid length of secret key"));
     }
+    if (msg.len == 0) {
+        nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "Empty data to sign"));
+    }
     ed25519_public_key pk;
     ed25519_publickey(*(const ed25519_secret_key *)sk.buf, pk);
     vstr_t vstr;
@@ -73,6 +76,9 @@ STATIC mp_obj_t mod_TrezorCrypto_Ed25519_verify(size_t n_args, const mp_obj_t *a
     if (sig.len != 64) {
         nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "Invalid length of signature"));
     }
+    if (msg.len == 0) {
+        nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "Empty data to verify"));
+    }
     return (0 == ed25519_sign_open(msg.buf, msg.len, *(const ed25519_public_key *)pk.buf, *(const ed25519_signature *)sig.buf)) ? mp_const_true : mp_const_false;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_TrezorCrypto_Ed25519_verify_obj, 4, 4, mod_TrezorCrypto_Ed25519_verify);
diff --git a/extmod/modtrezorcrypto/modtrezorcrypto-nist256p1.h b/extmod/modtrezorcrypto/modtrezorcrypto-nist256p1.h
index 78467b112e..a6b8889c29 100644
--- a/extmod/modtrezorcrypto/modtrezorcrypto-nist256p1.h
+++ b/extmod/modtrezorcrypto/modtrezorcrypto-nist256p1.h
@@ -55,6 +55,9 @@ STATIC mp_obj_t mod_TrezorCrypto_Nist256p1_sign(mp_obj_t self, mp_obj_t secret_k
     if (sk.len != 32) {
         nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "Invalid length of secret key"));
     }
+    if (msg.len == 0) {
+        nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "Empty data to sign"));
+    }
     vstr_t vstr;
     vstr_init_len(&vstr, 65);
     uint8_t pby;
@@ -82,6 +85,9 @@ STATIC mp_obj_t mod_TrezorCrypto_Nist256p1_verify(size_t n_args, const mp_obj_t
     if (sig.len != 65) {
         nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "Invalid length of signature"));
     }
+    if (msg.len == 0) {
+        nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "Empty data to verify"));
+    }
     return mp_obj_new_bool(0 == ecdsa_verify(&nist256p1, (const uint8_t *)pk.buf, (const uint8_t *)sig.buf, (const uint8_t *)msg.buf, msg.len));
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_TrezorCrypto_Nist256p1_verify_obj, 4, 4, mod_TrezorCrypto_Nist256p1_verify);
diff --git a/extmod/modtrezorcrypto/modtrezorcrypto-pbkdf2.h b/extmod/modtrezorcrypto/modtrezorcrypto-pbkdf2.h
index 1608e22aba..6bc976a35d 100644
--- a/extmod/modtrezorcrypto/modtrezorcrypto-pbkdf2.h
+++ b/extmod/modtrezorcrypto/modtrezorcrypto-pbkdf2.h
@@ -34,6 +34,13 @@ STATIC mp_obj_t mod_TrezorCrypto_Pbkdf2_make_new(const mp_obj_type_t *type, size
     mp_buffer_info_t salt;
     mp_get_buffer_raise(args[2], &salt, MP_BUFFER_READ);
 
+    if (password.len == 0) {
+        password.buf = "";
+    }
+    if (salt.len == 0) {
+        salt.buf = "";
+    }
+
     o->prf = 0;
     if (prf.len == 11 && memcmp(prf.buf, "hmac-sha256", prf.len) == 0) {
         pbkdf2_hmac_sha256_Init(&(o->ctx256), password.buf, password.len, salt.buf, salt.len);
diff --git a/extmod/modtrezorcrypto/modtrezorcrypto-ripemd160.h b/extmod/modtrezorcrypto/modtrezorcrypto-ripemd160.h
index bfae67dbca..5f88a0c858 100644
--- a/extmod/modtrezorcrypto/modtrezorcrypto-ripemd160.h
+++ b/extmod/modtrezorcrypto/modtrezorcrypto-ripemd160.h
@@ -43,7 +43,9 @@ STATIC mp_obj_t mod_TrezorCrypto_Ripemd160_update(mp_obj_t self, mp_obj_t data)
     mp_obj_Ripemd160_t *o = MP_OBJ_TO_PTR(self);
     mp_buffer_info_t msg;
     mp_get_buffer_raise(data, &msg, MP_BUFFER_READ);
-    ripemd160_Update(&(o->ctx), msg.buf, msg.len);
+    if (msg.len > 0) {
+        ripemd160_Update(&(o->ctx), msg.buf, msg.len);
+    }
     return mp_const_none;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_TrezorCrypto_Ripemd160_update_obj, mod_TrezorCrypto_Ripemd160_update);
diff --git a/extmod/modtrezorcrypto/modtrezorcrypto-secp256k1.h b/extmod/modtrezorcrypto/modtrezorcrypto-secp256k1.h
index 2837688578..0603f2fcf6 100644
--- a/extmod/modtrezorcrypto/modtrezorcrypto-secp256k1.h
+++ b/extmod/modtrezorcrypto/modtrezorcrypto-secp256k1.h
@@ -55,6 +55,9 @@ STATIC mp_obj_t mod_TrezorCrypto_Secp256k1_sign(mp_obj_t self, mp_obj_t secret_k
     if (sk.len != 32) {
         nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "Invalid length of secret key"));
     }
+    if (msg.len == 0) {
+        nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "Empty data to sign"));
+    }
     vstr_t vstr;
     vstr_init_len(&vstr, 65);
     uint8_t pby;
@@ -82,6 +85,9 @@ STATIC mp_obj_t mod_TrezorCrypto_Secp256k1_verify(size_t n_args, const mp_obj_t
     if (sig.len != 65) {
         nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "Invalid length of signature"));
     }
+    if (msg.len == 0) {
+        nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "Empty data to verify"));
+    }
     return mp_obj_new_bool(0 == ecdsa_verify(&secp256k1, (const uint8_t *)pk.buf, (const uint8_t *)sig.buf, (const uint8_t *)msg.buf, msg.len));
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_TrezorCrypto_Secp256k1_verify_obj, 4, 4, mod_TrezorCrypto_Secp256k1_verify);
diff --git a/extmod/modtrezorcrypto/modtrezorcrypto-sha256.h b/extmod/modtrezorcrypto/modtrezorcrypto-sha256.h
index 9f2d1aec8e..4a5a4b52c4 100644
--- a/extmod/modtrezorcrypto/modtrezorcrypto-sha256.h
+++ b/extmod/modtrezorcrypto/modtrezorcrypto-sha256.h
@@ -43,7 +43,9 @@ STATIC mp_obj_t mod_TrezorCrypto_Sha256_update(mp_obj_t self, mp_obj_t data) {
     mp_obj_Sha256_t *o = MP_OBJ_TO_PTR(self);
     mp_buffer_info_t msg;
     mp_get_buffer_raise(data, &msg, MP_BUFFER_READ);
-    sha256_Update(&(o->ctx), msg.buf, msg.len);
+    if (msg.len > 0) {
+        sha256_Update(&(o->ctx), msg.buf, msg.len);
+    }
     return mp_const_none;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_TrezorCrypto_Sha256_update_obj, mod_TrezorCrypto_Sha256_update);
diff --git a/extmod/modtrezorcrypto/modtrezorcrypto-sha3-256.h b/extmod/modtrezorcrypto/modtrezorcrypto-sha3-256.h
index 6af4d6240e..2a4026cbb9 100644
--- a/extmod/modtrezorcrypto/modtrezorcrypto-sha3-256.h
+++ b/extmod/modtrezorcrypto/modtrezorcrypto-sha3-256.h
@@ -43,7 +43,9 @@ STATIC mp_obj_t mod_TrezorCrypto_Sha3_256_update(mp_obj_t self, mp_obj_t data) {
     mp_obj_Sha3_256_t *o = MP_OBJ_TO_PTR(self);
     mp_buffer_info_t msg;
     mp_get_buffer_raise(data, &msg, MP_BUFFER_READ);
-    sha3_Update(&(o->ctx), msg.buf, msg.len);
+    if (msg.len > 0) {
+        sha3_Update(&(o->ctx), msg.buf, msg.len);
+    }
     return mp_const_none;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_TrezorCrypto_Sha3_256_update_obj, mod_TrezorCrypto_Sha3_256_update);
diff --git a/extmod/modtrezorcrypto/modtrezorcrypto-sha3-512.h b/extmod/modtrezorcrypto/modtrezorcrypto-sha3-512.h
index 68ced3ab60..0a66705a39 100644
--- a/extmod/modtrezorcrypto/modtrezorcrypto-sha3-512.h
+++ b/extmod/modtrezorcrypto/modtrezorcrypto-sha3-512.h
@@ -43,7 +43,9 @@ STATIC mp_obj_t mod_TrezorCrypto_Sha3_512_update(mp_obj_t self, mp_obj_t data) {
     mp_obj_Sha3_512_t *o = MP_OBJ_TO_PTR(self);
     mp_buffer_info_t msg;
     mp_get_buffer_raise(data, &msg, MP_BUFFER_READ);
-    sha3_Update(&(o->ctx), msg.buf, msg.len);
+    if (msg.len > 0) {
+        sha3_Update(&(o->ctx), msg.buf, msg.len);
+    }
     return mp_const_none;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_TrezorCrypto_Sha3_512_update_obj, mod_TrezorCrypto_Sha3_512_update);
diff --git a/extmod/modtrezorcrypto/modtrezorcrypto-sha512.h b/extmod/modtrezorcrypto/modtrezorcrypto-sha512.h
index 3faf0279e4..8de24f4711 100644
--- a/extmod/modtrezorcrypto/modtrezorcrypto-sha512.h
+++ b/extmod/modtrezorcrypto/modtrezorcrypto-sha512.h
@@ -42,7 +42,9 @@ STATIC mp_obj_t mod_TrezorCrypto_Sha512_update(mp_obj_t self, mp_obj_t data) {
     mp_obj_Sha512_t *o = MP_OBJ_TO_PTR(self);
     mp_buffer_info_t msg;
     mp_get_buffer_raise(data, &msg, MP_BUFFER_READ);
-    sha512_Update(&(o->ctx), msg.buf, msg.len);
+    if (msg.len > 0) {
+        sha512_Update(&(o->ctx), msg.buf, msg.len);
+    }
     return mp_const_none;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_TrezorCrypto_Sha512_update_obj, mod_TrezorCrypto_Sha512_update);
diff --git a/extmod/modtrezorcrypto/modtrezorcrypto-ssss.h b/extmod/modtrezorcrypto/modtrezorcrypto-ssss.h
index 3b33e5116c..df5fc30010 100644
--- a/extmod/modtrezorcrypto/modtrezorcrypto-ssss.h
+++ b/extmod/modtrezorcrypto/modtrezorcrypto-ssss.h
@@ -76,6 +76,9 @@ STATIC mp_obj_t mod_TrezorCrypto_SSSS_combine(mp_obj_t self, mp_obj_t shares) {
         if (MP_OBJ_IS_TYPE(share[i], &mp_type_bytes)) {
             mp_buffer_info_t s;
             mp_get_buffer_raise(share[i], &s, MP_BUFFER_READ);
+            if (s.len != 32) {
+                nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "Length of share has to be 256 bits"));
+            }
             bn_read_be(s.buf, &bnshares[n]);
         } else {
             memset(&bnshares[i], 0, sizeof(bignum256));
diff --git a/extmod/modtrezormsg/modtrezormsg-stmhal.h b/extmod/modtrezormsg/modtrezormsg-stmhal.h
index 770b2ca5a6..4467b900ac 100644
--- a/extmod/modtrezormsg/modtrezormsg-stmhal.h
+++ b/extmod/modtrezormsg/modtrezormsg-stmhal.h
@@ -29,7 +29,9 @@ ssize_t msg_recv(uint8_t *iface, uint8_t *buf, size_t len)
 ssize_t msg_send(uint8_t iface, const uint8_t *buf, size_t len)
 {
     (void)iface; // ignore interface for now
-    USBD_HID_SendReport(&hUSBDDevice, (uint8_t *)buf, len);
+    if (len > 0) {
+        USBD_HID_SendReport(&hUSBDDevice, (uint8_t *)buf, len);
+    }
     return len;
 }
 
diff --git a/extmod/modtrezormsg/modtrezormsg-unix.h b/extmod/modtrezormsg/modtrezormsg-unix.h
index 6b7f238b08..9ac622d916 100644
--- a/extmod/modtrezormsg/modtrezormsg-unix.h
+++ b/extmod/modtrezormsg/modtrezormsg-unix.h
@@ -54,8 +54,8 @@ ssize_t msg_recv(uint8_t *iface, uint8_t *buf, size_t len)
 ssize_t msg_send(uint8_t iface, const uint8_t *buf, size_t len)
 {
     (void)iface; // ignore interface for UDP
-    ssize_t r = -1;
-    if (slen) {
+    ssize_t r = len;
+    if (slen > 0) {
         r = sendto(s, buf, len, MSG_DONTWAIT, (const struct sockaddr *)&si_other, slen);
     }
     return r;
diff --git a/extmod/modtrezorui/modtrezorui-display.h b/extmod/modtrezorui/modtrezorui-display.h
index a9b99c708a..2cd9feceb3 100644
--- a/extmod/modtrezorui/modtrezorui-display.h
+++ b/extmod/modtrezorui/modtrezorui-display.h
@@ -81,7 +81,9 @@ STATIC mp_obj_t mod_TrezorUi_Display_blit(size_t n_args, const mp_obj_t *args) {
     if (data.len != 2 * w * h) {
         nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError, "Wrong data size (got %d bytes, expected %d bytes)", data.len, 2 * w * h));
     }
-    display_blit(x, y, w, h, data.buf, data.len);
+    if (w > 0 && h > 0) {
+        display_blit(x, y, w, h, data.buf, data.len);
+    }
     return mp_const_none;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_TrezorUi_Display_blit_obj, 6, 6, mod_TrezorUi_Display_blit);
@@ -157,7 +159,9 @@ STATIC mp_obj_t mod_TrezorUi_Display_text(size_t n_args, const mp_obj_t *args) {
     mp_int_t font = mp_obj_get_int(args[4]);
     mp_int_t fgcolor = mp_obj_get_int(args[5]);
     mp_int_t bgcolor = mp_obj_get_int(args[6]);
-    display_text(x, y, text.buf, text.len, font, fgcolor, bgcolor);
+    if (text.len > 0) {
+        display_text(x, y, text.buf, text.len, font, fgcolor, bgcolor);
+    }
     return mp_const_none;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_TrezorUi_Display_text_obj, 7, 7, mod_TrezorUi_Display_text);
@@ -175,7 +179,9 @@ STATIC mp_obj_t mod_TrezorUi_Display_text_center(size_t n_args, const mp_obj_t *
     mp_int_t font = mp_obj_get_int(args[4]);
     mp_int_t fgcolor = mp_obj_get_int(args[5]);
     mp_int_t bgcolor = mp_obj_get_int(args[6]);
-    display_text_center(x, y, text.buf, text.len, font, fgcolor, bgcolor);
+    if (text.len > 0) {
+        display_text_center(x, y, text.buf, text.len, font, fgcolor, bgcolor);
+    }
     return mp_const_none;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_TrezorUi_Display_text_center_obj, 7, 7, mod_TrezorUi_Display_text_center);
@@ -193,7 +199,9 @@ STATIC mp_obj_t mod_TrezorUi_Display_text_right(size_t n_args, const mp_obj_t *a
     mp_int_t font = mp_obj_get_int(args[4]);
     mp_int_t fgcolor = mp_obj_get_int(args[5]);
     mp_int_t bgcolor = mp_obj_get_int(args[6]);
-    display_text_right(x, y, text.buf, text.len, font, fgcolor, bgcolor);
+    if (text.len > 0) {
+        display_text_right(x, y, text.buf, text.len, font, fgcolor, bgcolor);
+    }
     return mp_const_none;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_TrezorUi_Display_text_right_obj, 7, 7, mod_TrezorUi_Display_text_right);
@@ -206,7 +214,10 @@ STATIC mp_obj_t mod_TrezorUi_Display_text_width(mp_obj_t self, mp_obj_t text, mp
     mp_buffer_info_t txt;
     mp_get_buffer_raise(text, &txt, MP_BUFFER_READ);
     mp_int_t f = mp_obj_get_int(font);
-    uint32_t w = display_text_width(txt.buf, txt.len, f);
+    uint32_t w = 0;
+    if (txt.len > 0) {
+        w = display_text_width(txt.buf, txt.len, f);
+    }
     return MP_OBJ_NEW_SMALL_INT(w);
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_3(mod_TrezorUi_Display_text_width_obj, mod_TrezorUi_Display_text_width);
@@ -225,7 +236,9 @@ STATIC mp_obj_t mod_TrezorUi_Display_qrcode(size_t n_args, const mp_obj_t *args)
     }
     mp_buffer_info_t data;
     mp_get_buffer_raise(args[3], &data, MP_BUFFER_READ);
-    display_qrcode(x, y, data.buf, data.len, scale);
+    if (data.len > 0) {
+        display_qrcode(x, y, data.buf, data.len, scale);
+    }
     return mp_const_none;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_TrezorUi_Display_qrcode_obj, 5, 5, mod_TrezorUi_Display_qrcode);
@@ -320,7 +333,9 @@ STATIC mp_obj_t mod_TrezorUi_Display_raw(mp_obj_t self, mp_obj_t reg, mp_obj_t d
     mp_int_t r = mp_obj_get_int(reg);
     mp_buffer_info_t raw;
     mp_get_buffer_raise(data, &raw, MP_BUFFER_READ);
-    display_raw(r, raw.buf, raw.len);
+    if (raw.len > 0) {
+        display_raw(r, raw.buf, raw.len);
+    }
     return mp_const_none;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_3(mod_TrezorUi_Display_raw_obj, mod_TrezorUi_Display_raw);
diff --git a/src/tests/run_tests.sh b/src/tests/run_tests.sh
index b29f4d1896..af36406eb0 100755
--- a/src/tests/run_tests.sh
+++ b/src/tests/run_tests.sh
@@ -1,7 +1,12 @@
 #!/bin/bash
 results=()
 error=0
-for i in test_*.py; do
+if [ -z "$1" ]; then
+    list="test_*.py"
+else
+    list="$1"
+fi
+for i in $list; do
    echo
     if ../../vendor/micropython/unix/micropython $i; then
        results+=("OK   $i")