(a) Reputation or Opinion Evidence. A witness’s credibility may be attacked or supported by testimony about the witness’s reputation for having a character for truthfulness or untruthfulness, or by testimony in the form of an opinion about that character. But evidence of truthful character is admissible only after the witness’s character for truthfulness has been attacked.
(b) Specific Instances of Conduct. Except for a criminal conviction under Rule 609, a party may not inquire into or offer extrinsic evidence to prove specific instances of the witness’s conduct in order to attack or support the witness’s character for truthfulness.