Callers must present a username and password or another authentication credential.The company's security policy states that: Some private conversations through Skype such as audio calls, text messages, and file sending (image, audio, or video) can make use of end-to-end encryption, but it may have to be manually turned on. Skype's encryption is inherent in the Skype Protocol and is transparent to callers. User public keys are certified by the Skype server at login with 1536-bit or 2048-bit RSA certificates. Skype reports that it uses 256 bit Advanced Encryption Standard (AES)/ Rijnadel encryption to communicate between Skype clients although when calling a telephone or mobile, the part of the call over the public switched telephone network ( PSTN) is not encrypted. Skype users can search for other users and send them messages. It is a peer-to-peer network where voice calls pass over the Internet rather than through a special-purpose network.

Skype is a Voice over Internet Protocol (VoIP) system developed by Skype Technologies S.A.

Password requirements for skype