Digital Envelop: As the name suggests, digital envelope is to seal the message in such a way that no one else other then the intended recipient can open the message. Practical implementation involves combination of symmetric key and public key methods, i.e. encrypting message using symmetric keys which in turn is protected using public key method. Digital envelops use symmetric keys to encrypt the message and assymetric keys to distribute the symmetric keys. Intention of Digital Envelope is to provide – Confidentiality & faster cryptographic operations.
Digital Signature: By digitally signing the message the recipient can make sure that message is from the intended sender and no one else has modified the message in transit. Digital signature uses both hashing algorithm and asymmetric encryption algorithm. First hash of the message is calculated and later the hash is encrypted using public key cryptography. Even a single bit change in original message results in entirely different hash. Few applications of digital signatures are digital certificates and binary sighning. Intention of Digital Certificate is to provide – authentication and integrity.
Digital Certificate: Digital envelope and digital signature do not ensure that public key being used is valid or belongs to intended recipient. Also they do not specify which hash and encryption algorithms are used. To eliminate this limitation, some third party (Certificate Authority) issues the certificate to user which binds the identity public key to its owner and also specifies additional parameter like algorithms used, validity period etc. Intention is to authenticate the public key and facilitate the use of public keys.
