A receiver non-committing encryption (RNCE) scheme [Canetti et al., STOC 1996; Canetti et al., TCC 2005] allows one to sample a public key \(\textsf{pk}\) and (dummy) ciphertext \(\textsf{ct}\) without knowing the message m. Later, when the message is known, one can sample a secret key \(\textsf{sk}\) that looks like the secret key corresponding to \(\textsf{pk}\) , and decryption of \(\textsf{ct}\) produces m. In this work, we study receiver non-committing identity-based encryption (RNC-IBE). We give constructions based on standard assumptions on bilinear groups (prior works [Hiroka et al., ASIACRYPT 2021] require indistinguishability obfuscation). Our RNC-IBE constructions have important implications for incompressible identity based encryption. This notion was recently introduced by Goyal et al., ITCS 2025. However, there were no constructions for the strongest security definitions in Goyal et al., ITCS 2025. Our RNC-IBE scheme also leads to the first incompressible IBE scheme with optimal ciphertext size, which was another open question in Goyal et al., ITCS 2025. We also give constructions for relaxed RNC-IBE (where the identity space is polynomial in the security parameter, but the public key is compact) that are based on \(\textsf{DDH, LWE}\) . This leads to a relaxed incompressible IBE scheme with strong security from the same assumptions.

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Non-committing Identity Based Encryption: Constructions and Applications

  • Rishab Goyal,
  • Fuyuki Kitagawa,
  • Venkata Koppula,
  • Ryo Nishimaki,
  • Mahesh Sreekumar Rajasree,
  • Takashi Yamakawa

摘要

A receiver non-committing encryption (RNCE) scheme [Canetti et al., STOC 1996; Canetti et al., TCC 2005] allows one to sample a public key \(\textsf{pk}\) and (dummy) ciphertext \(\textsf{ct}\) without knowing the message m. Later, when the message is known, one can sample a secret key \(\textsf{sk}\) that looks like the secret key corresponding to \(\textsf{pk}\) , and decryption of \(\textsf{ct}\) produces m. In this work, we study receiver non-committing identity-based encryption (RNC-IBE). We give constructions based on standard assumptions on bilinear groups (prior works [Hiroka et al., ASIACRYPT 2021] require indistinguishability obfuscation). Our RNC-IBE constructions have important implications for incompressible identity based encryption. This notion was recently introduced by Goyal et al., ITCS 2025. However, there were no constructions for the strongest security definitions in Goyal et al., ITCS 2025. Our RNC-IBE scheme also leads to the first incompressible IBE scheme with optimal ciphertext size, which was another open question in Goyal et al., ITCS 2025. We also give constructions for relaxed RNC-IBE (where the identity space is polynomial in the security parameter, but the public key is compact) that are based on \(\textsf{DDH, LWE}\) . This leads to a relaxed incompressible IBE scheme with strong security from the same assumptions.