diff --git a/algorithm-registry.md b/algorithm-registry.md
index 8809e2e..155c622 100644
--- a/algorithm-registry.md
+++ b/algorithm-registry.md
@@ -6,27 +6,51 @@ file **must** be reflected in the `PublicKeyDetails` enumeration in
 [`sigstore_common.proto`] in [sigstore/protobuf-specs].
 
 Sigstore clients aren't required to support all algorithms in this registry,
-and **MAY** support algorithms that aren't in the registry. However,
-compatibility with the Sigstore Public Good Instance requires support
-for at least one of these algorithms.
+and **MAY** support algorithms that aren't in the registry.
+
+See [Spec: Sigstore Public Deployment](./sigstore-public-deployment-spec.md)
+for the algorithms supported by Sigstore's public good instance.
+
+## Algorithm Purposes
+
+The following legend describes the purpose of each algorithm below.
+
+| Symbol | Description | Example |
+|--------|-------------| ------- |
+| 🔑     | End-user signing (ephemeral or long-lived keys) | A user signing with [`cosign`] |
+| 🔗     | TUF metadata signing | [sigstore/root-signing] |
+| 🔏     | Certificate authority materials (CA chains) | [Fulcio] |
+| 🪵     | Certificate transparency log materials (log keys and inclusion proofs) | Fulcio's [CT log] |
+| ⏰     | Timestamp authority materials (TSA chains and signed timestamps) | [sigstore/timestamp-authority] |
+| 📝     | Signature transparency log materials (log keys and inclusion proofs) | [Rekor] |
+| 👀     | Witness keys and signatures | Third-party log witnesses |
+
+[`cosign`]: https://github.com/sigstore/cosign
+[sigstore/root-signing]: https://github.com/sigstore/root-signing/
+[Fulcio]: https://github.com/sigstore/fulcio
+[CT log]: https://github.com/sigstore/fulcio#certificate-transparency
+[Rekor]: https://github.com/sigstore/rekor
+[sigstore/timestamp-authority]: https://github.com/sigstore/timestamp-authority
 
 ## Signature Algorithms
 
-| Algorithm | Name                       | Usage       | Notes                                                                            |
-|-----------|----------------------------|-------------| -------------------------------------------------------------------------------- |
-| RSA       | rsa-sign-pkcs1-2048-sha256 | verify only | Not recommended.                                                                 |
-|           | rsa-sign-pkcs1-3072-sha256 | sign/verify |                                                                                  |
-|           | rsa-sign-pkcs1-4096-sha256 | sign/verify |                                                                                  |
-|           | rsa-sign-pss-2048-sha256   | verify only | Not recommended.                                                                 |
-|           | rsa-sign-pss-3072-sha256   | sign/verify |                                                                                  |
-|           | rsa-sign-pss-4096-sha256   | sign/verify |                                                                                  |
-| ECDSA     | ecdsa-sha2-256-nistp256    | sign/verify |                                                                                  |
-|           | ecdsa-sha2-384-nistp384    | sign/verify |                                                                                  |
-|           | ecdsa-sha2-512-nistp521    | sign/verify |                                                                                  |
-| EdDSA     | ed25519                    | sign/verify |                                                                                  |
-|           | ed25519-ph                 | sign/verify | Recommended only for `hashedrekord`.                                             |
-| LMS       | lms-sha256                 | sign/verify | Stateful; signer selects the `H` parameter. Not recommended for keyless signing. |
-| LM-OTS    | lmots-sha256               | sign/verify | One-time use only; signer selects `n` and `w`.                                   |
+| Algorithm | Name                       | Usage       | Purpose | Notes                                                                            |
+|-----------|----------------------------|-------------| ------- |--------------------------------------------------------------------------------- |
+| RSA       | rsa-sign-pkcs1-2048-sha256 | verify only | 🔑 🪵   | Not recommended; not used for CT log materials outside of staging.               |
+|           | rsa-sign-pkcs1-3072-sha256 | sign/verify | 🔑      |                                                                                  |
+|           | rsa-sign-pkcs1-4096-sha256 | sign/verify | 🔑      |                                                                                  |
+|           | rsa-sign-pss-2048-sha256   | verify only | 🔑      | Not recommended.                                                                 |
+|           | rsa-sign-pss-3072-sha256   | sign/verify | 🔑      |                                                                                  |
+|           | rsa-sign-pss-4096-sha256   | sign/verify | 🔑      |                                                                                  |
+| ECDSA     | ecdsa-sha2-256-nistp256    | sign/verify | 🔑 🔗 🪵 📝 |                                                                               |
+|           | ecdsa-sha2-384-nistp384    | sign/verify | 🔑 🔏 ⏰ |                                                                                  |
+|           | ecdsa-sha2-256-nistp384    | verify only | 🔑      | Not recommended due to poor compatibility.                                       |
+|           | ecdsa-sha2-512-nistp521    | sign/verify | 🔑      |                                                                                  |
+|           | ecdsa-sha2-256-nistp521    | verify only | 🔑      | Not recommended due to poor compatibility.                                       |
+| EdDSA     | ed25519                    | sign/verify | 🔑 📝 👀 |                                                                                  |
+|           | ed25519-ph                 | sign/verify | 🔑      | Recommended only for `hashedrekord`.                                             |
+| LMS       | lms-sha256                 | sign/verify | 🔑      | Stateful; signer selects the `H` parameter. Not recommended for keyless signing. |
+| LM-OTS    | lmots-sha256               | sign/verify | 🔑      | One-time use only; signer selects `n` and `w`.                                   |
 
 ### Parameter configuration for LMS and LM-OTS
 
diff --git a/sigstore-public-deployment-spec.md b/sigstore-public-deployment-spec.md
index f386eb6..857f90f 100644
--- a/sigstore-public-deployment-spec.md
+++ b/sigstore-public-deployment-spec.md
@@ -191,3 +191,47 @@ The Sigstore project provides the resources necessary to deploy private Sigstore
 * [sigstore/scaffolding](https://github.com/sigstore/scaffolding)
 * [sigstore/sigstore-probers](https://github.com/sigstore/sigstore-probers)
 * [sigstore/policy-controller](https://github.com/sigstore/policy-controller)
+
+### 5.2 Supported Algorithms
+
+The Sigstore public good instance supports a subset of the algorithms defined
+in the [Algorithm Registry](./algorithm-registry.md). Clients that interoperate
+with the public good instance **MUST** support
+these algorithms in their respective contexts.
+
+#### 5.2.1 TUF
+
+The public good instance uses `ecdsa-sha2-256-nistp256` for all TUF signing keys.
+
+#### 5.2.2 Fulcio
+
+The public good instance uses `ecdsa-sha2-384-nistp384` for Fulcio's
+certificate chain and `ecdsa-sha2-256-nistp256` for Fulcio's certificate
+transparency log.
+
+Clients may submit Certificate Signing Requests (CSRs) with the following
+algorithms:
+
+| Algorithm                    | Required? | Recommended?  |
+|------------------------------|-----------|---------------|
+| `ecdsa-sha2-256-nistp256`    | Yes       | Yes           |
+| `ecdsa-sha2-384-nistp384`    | No        | Yes           |
+| `ecdsa-sha2-512-nistp521`    | No        | Yes           |
+| `rsa-sign-pkcs1-2048-sha256` | No        | No            |
+| `rsa-sign-pkcs1-3072-sha256` | No        | No            |
+| `rsa-sign-pkcs1-4096-sha256` | No        | No            |
+| `ed25519`                    | No        | Yes           |
+
+#### 5.2.3 Rekor
+
+The public good instance may use any of the following for Rekor's
+public key and signatures:
+
+* `ecdsa-sha2-256-nistp256` (Rekor v1)
+* `ecdsa-sha2-384-nistp384` (Rekor v1)
+* `ed25519` (beginning with Rekor v2)
+
+#### 5.2.4 Timestamp Authority
+
+The public good instance uses `ecdsa-sha2-384-nistp384` for the
+Timestamp Authority's certificate chain.