A rule-based attack is the most optimal technique in this scenario. This method enhances a standard dictionary attack by applying specific rules to the words in the list. Since it is known that the password contains the daughter's year of birth, a rule can be created to append a range of four-digit numbers representing years (e.g., 1990-2023) to common dictionary words. This approach is highly efficient because it leverages specific, known information about the password's structure, significantly narrowing the search space compared to more generic methods and increasing the probability of a quick success.

B. Brute force attack: This is suboptimal as it tries every possible character combination, ignoring the valuable clue about the year of birth, making it extremely time-consuming and inefficient.

C. Syllable attack: This technique combines syllables to form password guesses, which is not relevant for cracking a password known to contain a specific numerical pattern like a year.

D. Hybrid attack: While a rule-based attack is a type of hybrid attack, it is more specific. "Rule-based" is the better answer because it precisely describes using a predefined rule (appending a year) based on known information, making it the most optimal choice.

1. Weir, M., Aggarwal, S., de Medeiros, B., & Glodek, M. (2009). Password cracking using probabilistic context-free grammars. 2009 30th IEEE Symposium on Security and Privacy, 391-405. https://doi.org/10.1109/SP.2009.31. (This paper discusses advanced password cracking where rules are derived from password patterns, similar to the scenario. Section III.A describes how rules, such as appending digits, are fundamental to these attacks).

2. University of California, Berkeley. (2020). CS 161: Computer Security, Lecture 10: Web Security. "Password Cracking" section. The lecture notes describe dictionary attacks and modifications, stating, "Can augment with common rules (append '1', '123', etc.)." This principle directly applies to creating a rule for appending a known year.

3. Narayanan, A., & Shmatikov, V. (2005). Fast dictionary attacks on passwords using time-space tradeoff. Proceedings of the 12th ACM conference on Computer and communications security, 334-342. https://doi.org/10.1145/1102120.1102168. (This paper's introduction discusses how dictionary attacks are made more effective by applying "common transformations" or rules, such as adding digits, which is the core of a rule-based attack).