pkg/crypto: replace 'math/rand' with 'crypto/rand'

[bb7133]

What problem does this PR solve?

Replace math/rand with crypto/rand, which resolve some potential security vulnerability issue according to some third-party security scanners.

What is changed and how it works?

As described.

Check List

Tests

• No code

Code changes

• Has interface methods change

Side effects

• None

Related changes

• None

Release notes:

NONE

[ti-chi-bot]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-08-28 06:21:03.392835948 +0000 UTC m=+937658.527286064: ☑️ agreed by xhebox.