> For the complete documentation index, see [llms.txt](https://support.emsigner.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://support.emsigner.com/apis/signer-gateway/getting-started/key-concepts.md).

# Key Concepts

**Signing Sessions**

A signing session is a request sent to the signer gateway with one document or one or more hashes for the purpose of getting them signed. A unique reference is maintained for each signing session and gateway counters are deducted for successful signing sessions.

**Documents (or Hashes)**

The signer gateway accepts a document or a list of Hashes in either PDF or XML or Data formats for the purpose of getting them signed. If PDF documents are sent, the signer gateway automatically pads the visual appearance of the signature type selected back to the document

**Users and Subscription**

In the signer gateway, all transactions are associated with the user that purchased the signer gateway subscription (typically your administrator). Gateway logs are available on the dashboard for the purpose of reporting.

**Authentication**

The signer gateway authenticates incoming requests through a combination of app secret keys and user auth tokens.

**Data Encryption**

The signer gateway only accepts encrypted requests. All documents sent to the signer gateway must be encrypted with a random session key. Documents are also hashed and encrypted. The signer gateway validates that data has not been tampered in transit before allowing users to sign on documents.


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