import type { ErrorCause } from './error-cause.js';
/**
 * A condition that a verification method fails. A method that fails a condition cannot sign
 * a BTCR2 Update.
 */
export interface SigningMethodProblem {
    /** The field that fails the condition: `type`, `controller`, or `publicKeyMultibase`. */
    field: 'type' | 'controller' | 'publicKeyMultibase';
    /** The rule that the field breaks, for example `type must equal "Multikey"`. */
    message: string;
    /**
     * The type and the message of the key error: the decode error, or the error for text that
     * is not the base58btc encoding of the key.
     */
    cause?: ErrorCause;
}
/**
 * Returns the first condition that a verification method fails, or `undefined` if the method
 * can sign a BTCR2 Update. A method that fails a condition cannot sign. The specification
 * names the same three conditions on the write path ("Construct BTCR2 Signed Update") and on
 * the read path ("Check update.proof"):
 *
 * 1. `type` must equal {@link MULTIKEY_VERIFICATION_METHOD_TYPE | Multikey}.
 * 2. `controller` must equal the DID.
 * 3. `publicKeyMultibase` must encode a secp256k1 public key as the Multikey section of the
 *    BIP340 Cryptosuite specifies. That is: the `z` header, base58btc, 35 bytes, the prefix
 *    `0xe701`, and a valid compressed point. The `zQ3s` prefix alone does not satisfy this
 *    condition. The value must also be the base58btc text of the key. The decoder accepts
 *    some other text for the same bytes, but the specification allows no other encoding.
 *
 * The conditions apply to the method that signs, in the embedded form and in the referenced
 * form. The caller finds that method through `capabilityInvocation` first.
 *
 * @param {unknown} method The verification method that signs.
 * @param {string} did The DID: `sourceDidDocument.id` on the write path, the DID under resolution
 * on the read path, and the id of the resolved document for the aggregation communication key.
 * @returns {SigningMethodProblem | undefined} The first condition that fails, or `undefined`.
 */
export declare function signingMethodProblem(method: unknown, did: string): SigningMethodProblem | undefined;
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