Validate Security Certificate Format | Dataford Interview Questions

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Problem

At AegisCloud, certificate identifiers must follow a strict string format before they can be processed. Implement a function that returns True if a certificate string is valid and False otherwise.

Rules

A certificate string is valid if all of the following are true:

It contains exactly three non-empty segments separated by colons: header:payload:signature.
Each segment contains only uppercase letters (A-Z), digits (0-9), and the delimiter characters (, ), [, ], {, }.
Across the entire string, all delimiters are balanced and properly nested.
The string must not start or end with a colon, and it must not contain consecutive colons.

Formal Specification

Input: cert, a string
Output: bool — whether the certificate format is valid

Constraints

1 <= len(cert) <= 10^5
The input string contains ASCII characters
A valid certificate must contain exactly two colons
Each of the three segments must be non-empty

Function Signature

def validate_certificate(cert):