Methods and systems are provided that allow multiple identity-based digital signatures to be merged into a single identity-based "aggregate" digital signature. This identity-based aggregate signature has a shorter bit-length than the concatenation of the original unaggregated identity-based signatures. The identity-based aggregate signature can be verified by anyone who obtains the public keys of one or more Private Key Generators (PKGs), along with a description of which signer signed which message. The verifier does not need to obtain a different public key for each signer, since the signature scheme is "identity-based"; the number of PKGs may be fewer than the number of signers. Consequently, the total information needed to verify the identity-based aggregate signature--namely, a description of who signed what, the PKGs' public keys, and the identity-based aggregate signature itself--may be less than the information needed to verify separate digital signatures--namely, a description of who signed what, the public verification keys for all of the signers, and the concatenation of the signers' signatures. In some embodiments, the identity-based aggregate signature scheme has essentially the minimum-possible Kolmogorov complexity.