diff --git a/CMakeLists.txt b/CMakeLists.txt
index d564061..a9582d4 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -53,6 +53,7 @@ target_sources(pico_ccid PUBLIC
         ${CMAKE_CURRENT_LIST_DIR}/src/rng/neug.c
         ${CMAKE_CURRENT_LIST_DIR}/src/ccid/eac.c
         ${CMAKE_CURRENT_LIST_DIR}/src/ccid/crypto_utils.c
+        ${CMAKE_CURRENT_LIST_DIR}/src/ccid/asn1.c
         )
 
 target_include_directories(pico_ccid PUBLIC
diff --git a/src/ccid/asn1.c b/src/ccid/asn1.c
new file mode 100644
index 0000000..d0b5f7f
--- /dev/null
+++ b/src/ccid/asn1.c
@@ -0,0 +1,91 @@
+/* 
+ * This file is part of the Pico HSM distribution (https://github.com/polhenarejos/pico-hsm).
+ * Copyright (c) 2022 Pol Henarejos.
+ * 
+ * This program is free software: you can redistribute it and/or modify  
+ * it under the terms of the GNU General Public License as published by  
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but 
+ * WITHOUT ANY WARRANTY; without even the implied warranty of 
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License 
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "asn1.h"
+
+size_t asn1_len_tag(uint16_t tag, size_t len) {
+    size_t ret = 1+format_tlv_len(len, NULL)+len;
+    if (tag > 0x00ff)
+        return ret+1;
+    return ret;
+}
+
+int format_tlv_len(size_t len, uint8_t *out) {
+    if (len < 128) {
+        if (out)
+            *out = len;
+        return 1;
+    }
+    else if (len < 256) {
+        if (out) {
+            *out++ = 0x81;
+            *out++ = len;
+        }
+        return 2;
+    }
+    else {
+        if (out) {
+            *out++ = 0x82;
+            *out++ = (len >> 8) & 0xff;
+            *out++ = len & 0xff;
+        }
+        return 3;
+    }
+    return 0;
+}
+
+int walk_tlv(const uint8_t *cdata, size_t cdata_len, uint8_t **p, uint16_t *tag, size_t *tag_len, uint8_t **data) {
+    if (!p)
+        return 0;
+    if (!*p)
+        *p = (uint8_t *)cdata;
+    if (*p-cdata >= cdata_len)
+        return 0;
+    uint16_t tg = 0x0;
+    size_t tgl = 0;
+    tg = *(*p)++;
+    if ((tg & 0x1f) == 0x1f) {
+        tg <<= 8;
+        tg |= *(*p)++;
+    }    
+    tgl = *(*p)++;
+    if (tgl == 0x82) {
+        tgl = *(*p)++ << 8;
+        tgl |= *(*p)++;
+    }
+    else if (tgl == 0x81) {
+        tgl = *(*p)++;
+    }
+    if (tag)
+        *tag = tg;
+    if (tag_len)
+        *tag_len = tgl;
+    if (data)
+        *data = *p;
+    *p = *p+tgl;
+    return 1;
+}
+
+bool asn1_find_tag(const uint8_t *data, size_t data_len, uint16_t itag, size_t *tag_len, uint8_t **tag_data) {
+    uint16_t tag = 0x0;
+    uint8_t *p = NULL;
+    while (walk_tlv(data, data_len, &p, &tag, tag_len, tag_data)) {
+        if (itag == tag)
+            return true;
+    }
+    return false;
+}
diff --git a/src/ccid/asn1.h b/src/ccid/asn1.h
new file mode 100644
index 0000000..f22d754
--- /dev/null
+++ b/src/ccid/asn1.h
@@ -0,0 +1,29 @@
+/* 
+ * This file is part of the Pico HSM distribution (https://github.com/polhenarejos/pico-hsm).
+ * Copyright (c) 2022 Pol Henarejos.
+ * 
+ * This program is free software: you can redistribute it and/or modify  
+ * it under the terms of the GNU General Public License as published by  
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but 
+ * WITHOUT ANY WARRANTY; without even the implied warranty of 
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License 
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef _ASN1_H_
+#define _ASN1_H_
+
+#include <stdlib.h>
+#include "pico/stdlib.h"
+
+extern int walk_tlv(const uint8_t *cdata, size_t cdata_len, uint8_t **p, uint16_t *tag, size_t *tag_len, uint8_t **data);
+extern int format_tlv_len(size_t len, uint8_t *out);
+extern bool asn1_find_tag(const uint8_t *data, size_t data_len, uint16_t itag, size_t *tag_len, uint8_t **tag_data);
+extern size_t asn1_len_tag(uint16_t tag, size_t len);
+
+#endif
diff --git a/src/ccid/ccid2040.c b/src/ccid/ccid2040.c
index 45d5e44..3ffe1e6 100644
--- a/src/ccid/ccid2040.c
+++ b/src/ccid/ccid2040.c
@@ -529,79 +529,6 @@ void led_off_all() {
 #endif
 }
 
-size_t asn1_len_tag(uint16_t tag, size_t len) {
-    size_t ret = 1+format_tlv_len(len, NULL)+len;
-    if (tag > 0x00ff)
-        return ret+1;
-    return ret;
-}
-
-int format_tlv_len(size_t len, uint8_t *out) {
-    if (len < 128) {
-        if (out)
-            *out = len;
-        return 1;
-    }
-    else if (len < 256) {
-        if (out) {
-            *out++ = 0x81;
-            *out++ = len;
-        }
-        return 2;
-    }
-    else {
-        if (out) {
-            *out++ = 0x82;
-            *out++ = (len >> 8) & 0xff;
-            *out++ = len & 0xff;
-        }
-        return 3;
-    }
-    return 0;
-}
-
-int walk_tlv(const uint8_t *cdata, size_t cdata_len, uint8_t **p, uint16_t *tag, size_t *tag_len, uint8_t **data) {
-    if (!p)
-        return 0;
-    if (!*p)
-        *p = (uint8_t *)cdata;
-    if (*p-cdata >= cdata_len)
-        return 0;
-    uint16_t tg = 0x0;
-    size_t tgl = 0;
-    tg = *(*p)++;
-    if ((tg & 0x1f) == 0x1f) {
-        tg <<= 8;
-        tg |= *(*p)++;
-    }    
-    tgl = *(*p)++;
-    if (tgl == 0x82) {
-        tgl = *(*p)++ << 8;
-        tgl |= *(*p)++;
-    }
-    else if (tgl == 0x81) {
-        tgl = *(*p)++;
-    }
-    if (tag)
-        *tag = tg;
-    if (tag_len)
-        *tag_len = tgl;
-    if (data)
-        *data = *p;
-    *p = *p+tgl;
-    return 1;
-}
-
-bool asn1_find_tag(const uint8_t *data, size_t data_len, uint16_t itag, size_t *tag_len, uint8_t **tag_data) {
-    uint16_t tag = 0x0;
-    uint8_t *p = NULL;
-    while (walk_tlv(data, data_len, &p, &tag, tag_len, tag_data)) {
-        if (itag == tag)
-            return true;
-    }
-    return false;
-}
-
 void init_rtc() {
     
     rtc_init();
diff --git a/src/ccid/ccid2040.h b/src/ccid/ccid2040.h
index 4fb3509..5fc6d56 100644
--- a/src/ccid/ccid2040.h
+++ b/src/ccid/ccid2040.h
@@ -244,9 +244,4 @@ extern void led_set_blink(uint32_t mode);
 #define CCID_WRONG_PADDING                   -1011
 #define CCID_VERIFICATION_FAILED             -1012
 
-extern int walk_tlv(const uint8_t *cdata, size_t cdata_len, uint8_t **p, uint16_t *tag, size_t *tag_len, uint8_t **data);
-extern int format_tlv_len(size_t len, uint8_t *out);
-extern bool asn1_find_tag(const uint8_t *data, size_t data_len, uint16_t itag, size_t *tag_len, uint8_t **tag_data);
-extern size_t asn1_len_tag(uint16_t tag, size_t len);
-
 #endif
\ No newline at end of file
diff --git a/src/ccid/eac.c b/src/ccid/eac.c
index 09a8ccf..f1115f7 100644
--- a/src/ccid/eac.c
+++ b/src/ccid/eac.c
@@ -19,6 +19,7 @@
 #include "crypto_utils.h"
 #include "random.h"
 #include "mbedtls/cmac.h"
+#include "asn1.h"
 
 static uint8_t nonce[8];
 static uint8_t sm_kmac[16];
diff --git a/src/fs/file.c b/src/fs/file.c
index 96c81a1..e586be2 100644
--- a/src/fs/file.c
+++ b/src/fs/file.c
@@ -19,6 +19,7 @@
 #include "ccid2040.h"
 #include <string.h>
 #include <stdio.h>
+#include "asn1.h"
 
 extern const uintptr_t end_data_pool;
 extern const uintptr_t start_data_pool;