Glossary

Definitions of every technical and legal term used in District Seal documentation, in plain language.

A

Acoustic challenge

A verification step in which the signer is asked to speak a randomized set of words on camera. The audio is transcribed and compared to the words shown. See How It Works.

AdES — Advanced Electronic Signature

A category of electronic signature defined by EU Regulation 910/2014 (eIDAS). AdES signatures are uniquely linked to the signer, capable of identifying the signer, created under the signer's sole control, and linked to the signed data in a way that detects any later change.

AAL2 — Authenticator Assurance Level 2

One of three identity assurance levels defined by NIST SP 800-63-3. AAL2 requires two distinct authentication factors. District Seal's device binding (WebAuthn) plus biometrics maps to AAL2 design principles.

ArcFace

A family of deep-learning models for face recognition that produces a 512-dimensional vector representation of a face. Two faces are compared by measuring the cosine distance between their vectors.

ASR — Automatic Speech Recognition

Software that converts spoken audio into text. District Seal uses ASR to transcribe the signer's spoken challenge phrase.

B

BIPA

The Illinois Biometric Information Privacy Act (740 ILCS 14). One of the strictest biometric privacy statutes in the United States. It requires written notice, written release, a published retention schedule, and destruction of biometric data within three years of last interaction or when the initial purpose is satisfied, whichever comes first.

C

CCPA / CPRA

The California Consumer Privacy Act, as amended by the California Privacy Rights Act. It grants California residents rights over their personal information, including the right to know, delete, correct, and opt out of sale or sharing.

Certificate (in District Seal)

A PDF generated after a successful verification ceremony. It contains the document hash, the forensic event timeline, the results of each verification check, and a public verification URL.

Cosine distance

A measure of similarity between two vectors. 0 means identical direction, 1 means perpendicular, 2 means opposite. ArcFace uses cosine distance to compare face embeddings.

D

Device fingerprint

A short string derived from browser and device attributes (user agent, screen size, time zone, graphics renderer, canvas rendering behavior, and similar). Not a unique identifier but a stable signal used to recognize the same browser across sessions. Captured on every request to District Seal.

E

eIDAS

EU Regulation No 910/2014, "on electronic identification and trust services for electronic transactions in the internal market." Defines three levels of electronic signature: SES, AdES, and QES.

ESIGN Act

The Electronic Signatures in Global and National Commerce Act (15 U.S.C. § 7001 et seq.). A US federal statute establishing that signatures and records relating to interstate commerce may not be denied legal effect solely because they are electronic.

Embedding (face)

A fixed-length numeric vector representing a face. District Seal uses 512-dimensional ArcFace embeddings. An embedding cannot be reversed to reconstruct the original face image.

F

Forensic event log

A timestamped record of every step in a District Seal verification ceremony, including document scroll, consent, WebAuthn events, the acoustic challenge, liveness gestures, and the analysis results. Included in every certificate.

H

Hash (SHA-256)

A cryptographic function that maps any input to a fixed 256-bit output (64 hexadecimal characters). Any change to the input produces a completely different output. Used by District Seal to seal documents and certificates.

I

Identity distance

The cosine distance between the ArcFace embedding of the signer's live face and the embedding of the reference photo. Lower values mean a closer match. District Seal's default threshold is 0.55.

L

Liveness detection

The set of techniques used to confirm that a face presented to a camera belongs to a live, physically present person and not to a photograph, screen, mask, video replay, or synthetic deepfake.

M

MediaPipe Face Landmarker

An open-source library from Google that detects 468 facial landmarks in real time from a video stream. District Seal uses it client-side to compute head pose (pitch and yaw) during liveness gestures.

N

NIST SP 800-63-3

A NIST Special Publication defining digital identity guidelines, including Authenticator Assurance Levels (AAL1, AAL2, AAL3) and requirements for biometric authentication and presentation attack detection.

Q

QES — Qualified Electronic Signature

The highest category of electronic signature under eIDAS. Requires a certificate from a Qualified Trust Service Provider on an EU Trust List. District Seal does not issue QES.

R

Reference photo

The photograph the sender uploads before the signing ceremony. It becomes the enrollment template against which the signer's live face is compared.

S

SES — Simple Electronic Signature

The lowest category of electronic signature under eIDAS. Data in electronic form attached to or logically associated with other electronic data and used by the signatory to sign.

SHA-256

Secure Hash Algorithm 256-bit. See Hash above.

Svix

A webhook delivery and verification service. District Seal uses Svix's HMAC signature scheme to verify that incoming payment webhooks originate from Dodo Payments and not from a spoofed source.

U

UETA

The Uniform Electronic Transactions Act. A model statute adopted in 49 US states, DC, and the US Virgin Islands. Provides that records and signatures may not be denied legal effect solely because they are electronic, and defines how electronic signatures are attributed to a person.

W

WebAuthn

The World Wide Web Consortium standard for passwordless and multi-factor authentication using public-key cryptography. District Seal uses WebAuthn to bind a signing ceremony to a specific physical device — a phone, laptop, or hardware security key.