Confirm, corroborate, substantiate, verify, authenticate, validate mean to attest to the truth, genuineness, accuracy, or validity of something.
Confirm and corroborate are both used in reference to something doubtful or not yet proved.
Confirm, however, usually implies the resolving of all doubts typically by an authoritative statement or by indisputable facts.
Corroborate suggests particularly the strengthening of one statement or piece of evidence by another.
Substantiate presupposes something needing to be demonstrated or proved and implies the offering of evidence sufficient to sustain the contention or to create a strong presumption in its favor.
Verify has for its distinctive implication the established correspondence of the actual facts or details to those that are given in an account or statement. When what is in question is a suspicion, a fear, or a probability, it can be verified only in the result, event, or fulfillment.
In more general use verify implies a deliberate effort to establish the accuracy or truth of something usually by comparison (as with ascertainable facts, an original, or a series of control experiments).
Authenticate presupposes question of a thing’s genuineness or validity and therefore implies a demonstration of either of these by someone (as an expert or the proper authority) in a position to know or to determine.
Validate is more often used than authenticate when applied to legal papers requiring an official signature or seal before becoming valid. It is, however, also used when the soundness of a judgment, of a belief, or of a policy is in question.