* Present Perfect Tense: "I have striven" is correct. This tense is used to describe an action that started in the past and continues to the present.
* Past Participle: "Striven" is correct when used as a past participle in a sentence. For example, "Having striven for years, she finally achieved her goal."
In summary:
* Present Perfect: I have striven
* Past Participle: Striven