Validate the integrity of session recordings

BSR directories are validated based on the contents in the directory. Boundary cryptographically verifies each individual Boundary Session Recording (BSR) file. The keys used for verifying all Boundary Session Recording files are written to storage and wrapped by the KMS you configured. Each session recording has its own individual key. Boundary generates the following keys when a session recording is authorized:

• The BSR key is a plaintext AES-GCM key. It is not uploaded to the external object store.

• The private and public key pair is a ed25519 key pair. The key pair is not uploaded to the external object store.

The following files are stored in the BSR file structure to ensure the integrity of a session recording:

• bsrKey.pub is the public ed25519 key.
• wrappedBsrKey is the BSR key wrapped by the external KMS AES-GCM key that you configure.
• wrappedPrivKey is the private ed25519 key wrapped by the external KMS AES-GCM key that you configure.
• pubKeySelfSignature.sign is a self-signature of the plaintext public ed25519 key created with its private key.
• pubKeyBsrSignature.sign is a signature of the plaintext public ed25519 key created with the BSR key.
• SHA256SUM.sig is a signature of the plaintext SHA256SUM file created with the private key.

Encrypting the BSR key with an external KMS means that Boundary is not responsible for the longevity of the keys. The Boundary admin can always use that external KMS to unwrap the wrappedBsrKey and wrappedPrivKey. A BSR’s key is encrypted using the go-kms-wrapping package, and therefore the encrypted BlobInfo includes the metadata required to identify the key-version used during encryption. So if the wrapper is reinitialized properly, you can unwrap the keys even if the key has been rotated.

Each BSR directory contains a SHA256SUM and SHA256SUM.sig file that you can use to cryptographically verify the BSR directory's contents. The SHA256SUM file contains rows of file names paired with a checksum for the file contents. The SHA256SUM.sig is a copy of the SHA256SUM file, signed with the BSR's private key. Refer to the following example of a SHA256SUM file:

dc8ce2c42553ce510197c99efe21d89d6229feb4b49170511f49965f2e3cf1a3  wrappedBsrKey
a5a91b1b52fb53c4bab661b2e5846bb2a836f050e3d745e436078871914a0bc2  wrappedPrivKey
1ca281852ec0d447b94708f28a51b562d47b84affdba25e13a97b0fbd9126424  pubKeyBsrSignature.sign
7b5e18e5930bb4cce12a3f203328d9065cae29f26aba3963bb5faece2cf97231  pubKeySelfSignature.sign
dc7c6b1316624c7c486a22bab157f947df92b9f2ce4a72469b1f335399a043d5  bsrKey.pub
4d3966c458f4e5d67f9ac70b804540b927c718965267c3f36526bf0b18c40ad9  session-meta.json
6fec2173d331828677fb5e77fc19168daad3c5f0e82517a82e5701e6c2bdcbe1  session-recording.meta
ad76483e7cf3e65391a3a1d0b86a3ad436333ee225bea042b13900abc188b226  session-recording-summary.json

Follow these steps to validate a session recording:

1. Unwrap wrappedBsrKey using the external KMS you configured to retrieve the BSR key.
2. Unwrap wrappedPrivKey using the external KMS you configured to retrieve the private key.
3. Use the BSR key or the private key to verify the bsrKey.pub key using go-kms-wrapping HmacSha256(...).
4. When the key is verified, use the bsrKey.pub key to verify the BSR SHA256SUM file using go-kms-wrapping ed25519.Sign(...).