You can find the main changes over the last version in the first chapter of the specification: https://bugs.otr.im/otrv4/otrv4/-/blob/master/otrv4.md#main-chang

You can find the main changes over the last version in the first chapter of the specification: https://bugs.otr.im/otrv4/otrv4/-/blob/master/otrv4.md#main-changes-over-version-3 https://bugs.otr.im/otrv4/otrv4/-/blob/master/otrv4.md#main-... Quote: - Security level raised to 224 bits and based on Elliptic Curve Cryptography (ECC). - Additional protection against transcript decryption in the case of ECC compromise. - Support of conversations where one party is offline. - Updated cryptographic primitives and protocols: - Deniable authenticated key exchanges (DAKE) using "DAKE with Zero Knowledge" (DAKEZ) and "Extended Zero-knowledge Diffie-Hellman" (XZDH) [1]. DAKEZ corresponds to conversations when both parties are online (interactive) and XZDH to conversations when one of the parties is offline (non-interactive). - Key management using the Double Ratchet Algorithm [2]. - Upgraded SHA-1 and SHA-2 to SHAKE-256. - Switched from AES to ChaCha20 [3]. The RFC 7539 variant is used [16] . - Support of an out-of-order network model. - Support of different modes in which this specification can be implemented. - Explicit instructions for producing forged transcripts using the same functions used to conduct honest conversations.