---
title: SAIF.NetCore.SystemHash overview
summary: High-level purpose, scope, and responsibilities for this library.
status: draft
owner: SAIF Platform Team
last_reviewed: 2026-10-02
library: SAIF.NetCore.SystemHash
reference_type: package
---

# SAIF.NetCore.SystemHash overview

> **Documentation context:** NuGet package (pipeline-packed), consumed as `SAIF.NetCore.SystemHash` by application startup code and by `SAIF.NetCore.EnvironmentClient` and `SAIF.NetCore.OIDC` through the `ISystemHashService` interface only.

SAIF.NetCore.SystemHash is a single-class implementation-layer library that produces and validates a **system-hash caller-identity credential**: a SHA-256/Base64 digest of an application's assembly name and a `SystemType` classification, salted with a timestamp by `SAIF.NetCore.HashUtil`'s `SaltShaker`. Consumers present the salted credential to the external Environment API to retrieve secure settings or crypto configuration; this library also implements the server-side lifetime check that rejects an expired credential. It targets `net8.0` and `net10.0`.

## Purpose
- Issue a time-stamped, salted identity credential (`ComputeHash`, `Get`) that a calling application attaches to secure-setting requests.
- Compute the deterministic, unsalted identity hash (`ComputeHashNow`) that a validating service can compare a de-salted credential against.
- De-salt a previously issued credential and enforce its lifetime window (`RemoveSystemHashSaltAndValidateLifetime`), throwing `SystemHashExpiredException` (from `SAIF.NetCore.HashUtil`) when the credential is expired or not yet valid.

## Responsibilities
- Implement `ISystemHashService` (`SAIF.NetCore.ServiceContracts`) as the repository's sole concrete `SystemHashService`.
- Resolve the "system name" used in the identity hash from either an explicitly supplied `Assembly` (constructor) or `Assembly.GetCallingAssembly()`.
- Delegate the reversible salt/de-salt mechanics to `SAIF.NetCore.HashUtil`'s `SaltShaker`, while owning the create-timestamp selection and the lifetime decision itself.

## Key components
- `SystemHashService`: the library's only public type; implements all five `ISystemHashService` members and the private `GetHashValue` SHA-256 helper.

## Related documentation
- [Index](index.md)
- [Architecture](architecture.md)
- [Dependencies](dependencies.md)
- [Operations and processes](operations-processes.md)
- [Business rules](business-rules.md)
- [Security and authorization](security-authorization.md)
- [API reference](api/index.md)

## Sources
- `src/SAIF.NetCore.SystemHash/SAIF.NetCore.SystemHash/SAIF.NetCore.SystemHash/SAIF.NetCore.SystemHash.csproj`
- `src/SAIF.NetCore.SystemHash/SAIF.NetCore.SystemHash/SAIF.NetCore.SystemHash/SystemHashService.cs`
- `src/SAIF.NetCore.SystemHash/README.md`