- Ajatemplid digitaaldokumentidelBuldas, Ahto; Lipmaa, HelgerArvutimaailm1998 / 2, lk. 45-47: ill
- Eliminating counterevidence with applications to accountable certificate managementBuldas, Ahto; Laud, Peeter; Lipmaa, HelgerJournal of computer security2002 / 3, p. 273-296 https://content.iospress.com/articles/journal-of-computer-security/jcs161
- Time-stamping with binary linking schemesBuldas, Ahto; Laud, Peeter; Lipmaa, Helger; Willemson, JanAdvances in Cryptology : CRYPTO'98 : 18th Annual International Cryptology Conference, Santa Barbara, California, USA August 23–27, 1998 : proceedings1998 / p. 486-501 : ill