diff --git a/fido2/ctaphid.c b/fido2/ctaphid.c
index 6452cde..4fa4ab0 100644
--- a/fido2/ctaphid.c
+++ b/fido2/ctaphid.c
@@ -534,6 +534,10 @@ static int ctaphid_buffer_packet(uint8_t * pkt_raw, uint8_t * cmd, uint32_t * ci
     return buffer_status();
 }
 
+extern void _check_ret(CborError ret, int line, const char * filename);
+#define check_hardcore(r)   _check_ret(r,__LINE__, __FILE__);\
+                            if ((r) != CborNoError) exit(1);
+
 uint8_t ctaphid_handle_packet(uint8_t * pkt_raw)
 {
     uint8_t cmd;
@@ -725,7 +729,134 @@ uint8_t ctaphid_handle_packet(uint8_t * pkt_raw)
             is_busy = 0;
         break;
 #endif
-#if defined(SOLO_HACKER)
+#if defined(SOLO_HACKER) && (DEBUG_LEVEL > 0)
+        case CTAPHID_PROBE:
+
+            /*
+             * Expects CBOR-serialized data of the form
+             * {"subcommand": "hash_type", "data": b"the_data"}
+             * with hash_type in SHA256, SHA512
+             */
+
+            // some random logging
+            printf1(TAG_HID,"CTAPHID_PROBE\n");
+            // initialise CTAP response object
+            ctap_response_init(&ctap_resp);
+            // initialise write buffer
+            ctaphid_write_buffer_init(&wb);
+            wb.cid = cid;
+            wb.cmd = CTAPHID_PROBE;
+
+            // prepare parsing (or halt)
+            int ret;
+            CborParser parser;
+            CborValue it, map;
+            ret = cbor_parser_init(
+                ctap_buffer, (size_t) buffer_len(),
+                // strictly speaking, CTAP is not RFC canonical...
+                CborValidateCanonicalFormat,
+                &parser, &it);
+            check_hardcore(ret);
+
+            CborType type = cbor_value_get_type(&it);
+            if (type != CborMapType) exit(1);
+
+            ret = cbor_value_enter_container(&it,&map);
+            check_hardcore(ret);
+
+            size_t map_length = 0;
+            ret = cbor_value_get_map_length(&it, &map_length);
+            if (map_length != 2) exit(1);
+
+            // parse subcommand (or halt)
+            CborValue val;
+            ret = cbor_value_map_find_value(&it, "subcommand", &val);
+            check_hardcore(ret);
+            if (!cbor_value_is_text_string(&val))
+                exit(1);
+
+            int sha_version = 0;
+            bool found = false;
+            if (!found) {
+                ret = cbor_value_text_string_equals(
+                        &val, "SHA256", &found);
+                check_hardcore(ret);
+                if (found)
+                    sha_version = 256;
+            }
+            if (!found) {
+                ret = cbor_value_text_string_equals(
+                        &val, "SHA512", &found);
+                check_hardcore(ret);
+                if (found)
+                    sha_version = 512;
+            }
+            if (sha_version == 0)
+                exit(1);
+
+            // parse data (or halt)
+            ret = cbor_value_map_find_value(&it, "data", &val);
+            check_hardcore(ret);
+            if (!cbor_value_is_byte_string(&val))
+                exit(1);
+
+            size_t data_length = 0;
+            ret = cbor_value_calculate_string_length(&val, &data_length);
+            check_hardcore(ret);
+            if (data_length > 6*1024)
+                exit(1);
+
+            unsigned char data[6*1024];
+            ret = cbor_value_copy_byte_string (
+                    &val, &data[0], &data_length, &val);
+            check_hardcore(ret);
+
+            // execute subcommand
+            if (sha_version == 256) {
+                // calculate hash
+                crypto_sha256_init();
+                crypto_sha256_update(data, data_length);
+                crypto_sha256_final(ctap_buffer);
+                // write output
+                wb.bcnt = CF_SHA256_HASHSZ;  // 32 bytes
+                ctaphid_write(&wb, &ctap_buffer, CF_SHA256_HASHSZ);
+            }
+
+            if (sha_version == 512) {
+                // calculate hash
+                crypto_sha512_init();
+                crypto_sha512_update(data, data_length);
+                crypto_sha512_final(ctap_buffer);
+                // write output
+                wb.bcnt = CF_SHA512_HASHSZ;  // 64 bytes
+                ctaphid_write(&wb, &ctap_buffer, CF_SHA512_HASHSZ);
+            }
+
+            // finalize
+            ctaphid_write(&wb, NULL, 0);
+            is_busy = 0;
+        break;
+
+        /*
+        case CTAPHID_SHA256:
+            // some random logging
+            printf1(TAG_HID,"CTAPHID_SHA256\n");
+            // initialise CTAP response object
+            ctap_response_init(&ctap_resp);
+            // initialise write buffer
+            ctaphid_write_buffer_init(&wb);
+            wb.cid = cid;
+            wb.cmd = CTAPHID_SHA256;
+            wb.bcnt = CF_SHA256_HASHSZ;  // 32 bytes
+            // calculate hash
+            crypto_sha256_init();
+            crypto_sha256_update(ctap_buffer, buffer_len());
+            crypto_sha256_final(ctap_buffer);
+            // copy to output
+            ctaphid_write(&wb, &ctap_buffer, CF_SHA256_HASHSZ);
+            ctaphid_write(&wb, NULL, 0);
+            is_busy = 0;
+        break;
         case CTAPHID_SHA512:
             // some random logging
             printf1(TAG_HID,"CTAPHID_SHA512\n");
@@ -745,6 +876,7 @@ uint8_t ctaphid_handle_packet(uint8_t * pkt_raw)
             ctaphid_write(&wb, NULL, 0);
             is_busy = 0;
         break;
+        */
 #endif
         default:
             printf2(TAG_ERR,"error, unimplemented HID cmd: %02x\r\n", buffer_cmd());
diff --git a/fido2/ctaphid.h b/fido2/ctaphid.h
index 7224ca5..135260b 100644
--- a/fido2/ctaphid.h
+++ b/fido2/ctaphid.h
@@ -28,8 +28,8 @@
 #define CTAPHID_ENTERBOOT       (TYPE_INIT | 0x51)
 #define CTAPHID_ENTERSTBOOT     (TYPE_INIT | 0x52)
 #define CTAPHID_GETRNG          (TYPE_INIT | 0x60)
-#define CTAPHID_SHA256          (TYPE_INIT | 0x70)  // not implemented
-#define CTAPHID_SHA512          (TYPE_INIT | 0x71)
+// reserved for debug, not implemented except for HACKER and DEBUG_LEVEl > 0
+#define CTAPHID_PROBE           (TYPE_INIT | 0x70)
 
     #define ERR_INVALID_CMD         0x01
     #define ERR_INVALID_PAR         0x02
diff --git a/targets/stm32l432/Makefile b/targets/stm32l432/Makefile
index 0ac5843..19abebd 100644
--- a/targets/stm32l432/Makefile
+++ b/targets/stm32l432/Makefile
@@ -15,6 +15,12 @@ merge_hex=../../tools/solotool.py mergehex
 firmware-hacker:
 	$(MAKE) -f $(APPMAKE) -j8 solo.hex PREFIX=$(PREFIX) DEBUG=0 EXTRA_DEFINES='-DSOLO_HACKER -DFLASH_ROP=0'
 
+firmware-hacker-debug-1:
+	$(MAKE) -f $(APPMAKE) -j8 solo.hex PREFIX=$(PREFIX) DEBUG=1 EXTRA_DEFINES='-DSOLO_HACKER -DFLASH_ROP=0'
+
+firmware-hacker-debug-2:
+	$(MAKE) -f $(APPMAKE) -j8 solo.hex PREFIX=$(PREFIX) DEBUG=2 EXTRA_DEFINES='-DSOLO_HACKER -DFLASH_ROP=0'
+
 firmware-secure:
 	$(MAKE) -f $(APPMAKE) -j8 solo.hex PREFIX=$(PREFIX) DEBUG=0 EXTRA_DEFINES='-DUSE_SOLOKEYS_CERT -DFLASH_ROP=2'