MPP.BodyDigest (mpp v0.6.0)

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SHA-256 body digest computation and verification.

Produces digest strings in the format "sha-256=<base64>" for binding request bodies to challenges. Maps are JSON-encoded before hashing. Verification uses constant-time comparison to prevent timing attacks.

Note: When passing a map, the digest is computed over Jason.encode!/1 output. For request body binding, pass the raw body bytes to ensure the digest matches the exact wire format. The map convenience path matches the mppx TypeScript reference but may produce different digests than raw body strings if key ordering differs.

Examples

iex> MPP.BodyDigest.compute(~s({"amount":"1000"}))
"sha-256=" <> _base64

iex> digest = MPP.BodyDigest.compute(%{"amount" => "1000"})
iex> MPP.BodyDigest.verify(digest, %{"amount" => "1000"})
true

API Functions

FunctionArityDescriptionParam Kinds
verify2Verify a digest matches the given body using constant-time comparison.digest: value, body: value
compute1Compute a SHA-256 digest of the given body.body: value

Summary

Functions

compute(body)

Compute a SHA-256 digest of the given body.

verify(digest, body)

Verify a digest matches the given body using constant-time comparison.

Functions

compute(body)

@spec compute(String.t() | map()) :: String.t()
@spec compute(map()) :: String.t()

Compute a SHA-256 digest of the given body.

Parameters

  • body - Request body as a string or map (maps are JSON-encoded before hashing) (value)

Returns

Digest string in format "sha-256=<base64>" (string)

Composes With

  • verify
# descripex:contract
%{
  params: %{
    body: %{
      description: "Request body as a string or map (maps are JSON-encoded before hashing)",
      kind: :value
    }
  },
  returns: %{
    type: :string,
    description: "Digest string in format \"sha-256=<base64>\"",
    example: "sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE"
  },
  composes_with: [:verify]
}

verify(digest, body)

@spec verify(String.t(), String.t() | map()) :: boolean()

Verify a digest matches the given body using constant-time comparison.

Parameters

  • digest - Digest string to verify (e.g., "sha-256=...") (value)
  • body - Request body as a string or map (maps are JSON-encoded before hashing) (value)

Returns

True if the digest matches, false otherwise (boolean)

Composes With

  • compute
# descripex:contract
%{
  params: %{
    body: %{
      description: "Request body as a string or map (maps are JSON-encoded before hashing)",
      kind: :value
    },
    digest: %{
      description: "Digest string to verify (e.g., \"sha-256=...\")",
      kind: :value
    }
  },
  returns: %{
    type: :boolean,
    description: "True if the digest matches, false otherwise"
  },
  composes_with: [:compute]
}