# Boundary node http response headers

**URL:** <https://forum.dfinity.org/t/boundary-node-http-response-headers/10747>\
**Category:** Developers\
**Created:** [February 7, 2022, 4:21pm UTC](https://forum.dfinity.org/t/boundary-node-http-response-headers/10747 "2022-02-07T16:21:52Z")\
**Posts on this page:** 1\
**Showing post:** 45

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**Author:** ![nomeata](https://sea1.discourse-cdn.com/flex023/user_avatar/forum.dfinity.org/nomeata/32/733_2.png) [@nomeata](https://forum.dfinity.org/u/nomeata)\
**Post date:** [February 11, 2022, 9:32pm UTC](https://forum.dfinity.org/t/boundary-node-http-response-headers/10747/45 "2022-02-11T21:32:34Z")

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I don’t quite understand the question. The certification needs to build a trust path between something that the user (the service work) knows, namely the IC root key, and the file just loaded. This involves a few steps (root public key → subnet public key → subnet state merkle tree root → subnet state merkle tree entry with certified data from canister → canister merkle tree root → canister merkle tree entry with sha256 of file loaded → file), and one of the steps requires the SHA256 signature of the file. So the canister needs the SHA256. Also see this video for more details:

[![](https://us1.discourse-cdn.com/flex023/uploads/dfn/original/2X/b/bd8d2cffd9c4f56b6c47f153924fec22d570ab3a.jpeg "Inside the Internet Computer | Certified Variables") ](https://www.youtube.com/watch?v=mZbFhRIHIiY)

Is it the case that the default asset canister doesn’t calculate the SHA256 upon upload, but requires the uploader to set it? Then that’s an engineering choice around that canister.

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