esp enc -> subdir

esp_encrypted_img/README.md

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+# ESP Encrypted Image Abstraction Layer
+
+[![Component Registry](https://components.espressif.com/components/espressif/esp_encrypted_img/badge.svg)](https://components.espressif.com/components/espressif/esp_encrypted_img)
+
+This component provides an API interface to decrypt data defined in "ESP Encrypted Image" format. This format is as specified at [Image Format](#image-format)
+
+This component can help in integrating pre encrypted firmware in over-the-air updates. Additionally, this component can also be used for other use-cases which requires addition of encryption layer for custom data.
+
+
+## Image Format
+
+![Image Format](https://raw.githubusercontent.com/espressif/idf-extra-components/master/esp_encrypted_img/image_format.png)
+
+```c
+typedef struct {
+    char magic[4];
+    char enc_gcm[384];
+    char iv[16];
+    char bin_size[4];
+    char auth[16];
+    char extra_header[88];
+} pre_enc_bin_header;
+```
+
+The above struct represents encrypted image header.
+
+Note:
+* RSA-3072 key is provided to the tool externally. You can generate RSA key pair using following command:
+
+    `openssl genrsa -out rsa_key/private.pem 3072`
+
+* AES-GCM key and IV are generated by the tool itself.
+
+## Tool Info
+
+This component also contains tool ([esp_enc_img_gen.py](https://github.com/espressif/idf-extra-components/blob/master/esp_encrypted_img/tools/esp_enc_img_gen.py)) to generate encrypted images using RSA3072 public key.
+
+### Encrypt the image
+
+```
+python esp_enc_img_gen.py encrypt /path/to/input.bin /path/to/RSA-public-key /path/to/enc.bin
+```
+
+### Decrypt the image
+```
+python esp_enc_img_gen.py decrypt /path/to/enc.bin /path/to/RSA-private-key /path/to/output.bin
+```
+
+
+To know more about the tool, use command:
+`python esp_enc_img-gen.py --help`
+
+
+## API Reference
+
+To learn more about how to use this component, please check API Documentation from header file [esp_encrypted_img.h](https://github.com/espressif/idf-extra-components/blob/master/esp_encrypted_img/include/esp_encrypted_img.h)