diff --git a/scripts/imgtool/image.py b/scripts/imgtool/image.py
index 2ad5538..adba2b1 100644
--- a/scripts/imgtool/image.py
+++ b/scripts/imgtool/image.py
@@ -1,6 +1,6 @@
 # Copyright 2018 Nordic Semiconductor ASA
 # Copyright 2017 Linaro Limited
-# Copyright 2019 Arm Limited
+# Copyright 2019-2020 Arm Limited
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -61,7 +61,8 @@
         'ENCRSA2048': 0x30,
         'ENCKW128': 0x31,
         'ENCEC256': 0x32,
-        'DEPENDENCY': 0x40
+        'DEPENDENCY': 0x40,
+        'SEC_CNT': 0x50,
 }
 
 TLV_SIZE = 4
@@ -119,7 +120,7 @@
                  pad_header=False, pad=False, align=1, slot_size=0,
                  max_sectors=DEFAULT_MAX_SECTORS, overwrite_only=False,
                  endian="little", load_addr=0, erased_val=None,
-                 save_enctlv=False):
+                 save_enctlv=False, security_counter=None):
         self.version = version or versmod.decode_version("0")
         self.header_size = header_size
         self.pad_header = pad_header
@@ -137,12 +138,23 @@
         self.save_enctlv = save_enctlv
         self.enctlv_len = 0
 
+        if security_counter == 'auto':
+            # Security counter has not been explicitly provided,
+            # generate it from the version number
+            self.security_counter = ((self.version.major << 24)
+                                     + (self.version.minor << 16)
+                                     + self.version.revision)
+        else:
+            self.security_counter = security_counter
+
     def __repr__(self):
-        return "<Image version={}, header_size={}, base_addr={}, load_addr={}, \
-                align={}, slot_size={}, max_sectors={}, overwrite_only={}, \
-                endian={} format={}, payloadlen=0x{:x}>".format(
+        return "<Image version={}, header_size={}, security_counter={}, \
+                base_addr={}, load_addr={}, align={}, slot_size={}, \
+                max_sectors={}, overwrite_only={}, endian={} format={}, \
+                payloadlen=0x{:x}>".format(
                     self.version,
                     self.header_size,
+                    self.security_counter,
                     self.base_addr if self.base_addr is not None else "N/A",
                     self.load_addr,
                     self.align,
@@ -246,14 +258,22 @@
     def create(self, key, enckey, dependencies=None):
         self.enckey = enckey
 
-        if dependencies is None:
-            dependencies_num = 0
-            protected_tlv_size = 0
-        else:
-            # Size of a Dependency TLV = Header ('BBH') + Payload('IBBHI')
-            # = 16 Bytes
+        protected_tlv_size = 0
+
+        if self.security_counter is not None:
+            # Size of the security counter TLV: header ('HH') + payload ('I')
+            #                                   = 4 + 4 = 8 Bytes
+            protected_tlv_size += TLV_SIZE + 4
+
+        if dependencies is not None:
+            # Size of a Dependency TLV = Header ('HH') + Payload('IBBHI')
+            # = 4 + 12 = 16 Bytes
             dependencies_num = len(dependencies[DEP_IMAGES_KEY])
-            protected_tlv_size = (dependencies_num * 16) + TLV_INFO_SIZE
+            protected_tlv_size += (dependencies_num * 16)
+
+        if protected_tlv_size != 0:
+            # Add the size of the TLV info header
+            protected_tlv_size += TLV_INFO_SIZE
 
         # At this point the image is already on the payload, this adds
         # the header to the payload as well
@@ -265,17 +285,24 @@
         # in the hash calculation
         protected_tlv_off = None
         if protected_tlv_size != 0:
-            for i in range(dependencies_num):
-                e = STRUCT_ENDIAN_DICT[self.endian]
-                payload = struct.pack(
-                                e + 'B3x'+'BBHI',
-                                int(dependencies[DEP_IMAGES_KEY][i]),
-                                dependencies[DEP_VERSIONS_KEY][i].major,
-                                dependencies[DEP_VERSIONS_KEY][i].minor,
-                                dependencies[DEP_VERSIONS_KEY][i].revision,
-                                dependencies[DEP_VERSIONS_KEY][i].build
-                                )
-                prot_tlv.add('DEPENDENCY', payload)
+
+            e = STRUCT_ENDIAN_DICT[self.endian]
+
+            if self.security_counter is not None:
+                payload = struct.pack(e + 'I', self.security_counter)
+                prot_tlv.add('SEC_CNT', payload)
+
+            if dependencies is not None:
+                for i in range(dependencies_num):
+                    payload = struct.pack(
+                                    e + 'B3x'+'BBHI',
+                                    int(dependencies[DEP_IMAGES_KEY][i]),
+                                    dependencies[DEP_VERSIONS_KEY][i].major,
+                                    dependencies[DEP_VERSIONS_KEY][i].minor,
+                                    dependencies[DEP_VERSIONS_KEY][i].revision,
+                                    dependencies[DEP_VERSIONS_KEY][i].build
+                                    )
+                    prot_tlv.add('DEPENDENCY', payload)
 
             protected_tlv_off = len(self.payload)
             self.payload += prot_tlv.get()
diff --git a/scripts/imgtool/main.py b/scripts/imgtool/main.py
index 5ef7943..2c7cc2a 100755
--- a/scripts/imgtool/main.py
+++ b/scripts/imgtool/main.py
@@ -1,7 +1,7 @@
 #! /usr/bin/env python3
 #
 # Copyright 2017 Linaro Limited
-# Copyright 2019 Arm Limited
+# Copyright 2019-2020 Arm Limited
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -154,6 +154,20 @@
         raise click.BadParameter("{}".format(e))
 
 
+def validate_security_counter(ctx, param, value):
+    if value is not None:
+        if value.lower() == 'auto':
+            return 'auto'
+        else:
+            try:
+                return int(value, 0)
+            except ValueError:
+                raise click.BadParameter(
+                    "{} is not a valid integer. Please use code literals "
+                    "prefixed with 0b/0B, 0o/0O, or 0x/0X as necessary."
+                    .format(value))
+
+
 def validate_header_size(ctx, param, value):
     min_hdr_size = image.IMAGE_HEADER_SIZE
     if value < min_hdr_size:
@@ -190,13 +204,11 @@
 
     def convert(self, value, param, ctx):
         try:
-            if value[:2].lower() == '0x':
-                return int(value[2:], 16)
-            elif value[:1] == '0':
-                return int(value, 8)
-            return int(value, 10)
+            return int(value, 0)
         except ValueError:
-            self.fail('%s is not a valid integer' % value, param, ctx)
+            self.fail('%s is not a valid integer. Please use code literals '
+                      'prefixed with 0b/0B, 0o/0O, or 0x/0X as necessary.'
+                      % value, param, ctx)
 
 
 @click.argument('outfile')
@@ -233,6 +245,9 @@
 @click.option('-d', '--dependencies', callback=get_dependencies,
               required=False, help='''Add dependence on another image, format:
               "(<image_ID>,<image_version>), ... "''')
+@click.option('-s', '--security-counter', callback=validate_security_counter,
+              help='Specify the value of security counter. Use the `auto` '
+              'keyword to automatically generate it from the image version.')
 @click.option('-v', '--version', callback=validate_version,  required=True)
 @click.option('--align', type=click.Choice(['1', '2', '4', '8']),
               required=True)
@@ -242,13 +257,15 @@
                .hex extension, otherwise binary format is used''')
 def sign(key, align, version, header_size, pad_header, slot_size, pad,
          max_sectors, overwrite_only, endian, encrypt, infile, outfile,
-         dependencies, load_addr, hex_addr, erased_val, save_enctlv):
+         dependencies, load_addr, hex_addr, erased_val, save_enctlv,
+         security_counter):
     img = image.Image(version=decode_version(version), header_size=header_size,
                       pad_header=pad_header, pad=pad, align=int(align),
                       slot_size=slot_size, max_sectors=max_sectors,
                       overwrite_only=overwrite_only, endian=endian,
                       load_addr=load_addr, erased_val=erased_val,
-                      save_enctlv=save_enctlv)
+                      save_enctlv=save_enctlv,
+                      security_counter=security_counter)
     img.load(infile)
     key = load_key(key) if key else None
     enckey = load_key(encrypt) if encrypt else None