PGP Overview 2004/11/30 Information-Center meeting peterkim

servers POP3: Post Office Protocol, port #110 IMAP: Internet Mail Access Protocol, port #143 SMTP: Simple Main Transfer Protocol, port #25

Pretty good privacy (PGP) Internet encryption scheme, de-facto standard. uses symmetric key cryptography, public key cryptography, hash function, and digital signature as described. provides secrecy, sender authentication, integrity. inventor, Phil Zimmerman, a undergraduate from FAU in BEGIN PGP SIGNED MESSAGE-- - Hash: SHA1 Bob:My husband is out of town tonight.Passionately yours, Alice ---BEGIN PGP SIGNATURE--- Version: PGP 5.0 Charset: noconv yhHJRHhGJGhgg/12EpJ+lo8gE4vB3 mqJhFEvZP9t6n7G6m5Gw2 ---END PGP SIGNATURE--- A PGP signed message:

PGP overview — mechanism Anybody creates his/her RSA public key and private key (512, 768, or 1024 bits) (automatically generated by PGP) Anybody (e.g., Alice) can send encrypted (as well as signed) to anybody else (e.g., Bob).  Generate a one-time random key to encrypt the using a secret key system (e.g., IDEA)  Encrypt the random key with Bob ’ s public key  May sign the with her own private key  May compress the before encryption Bob can use his private key to decrypt the encrypted .  Moreover, “ pass phrase ” is required for decryption  The “ pass phrase ” is typed by Bob when PGP generates RSA keys for him

PGP overview — key distribution Public key system (RSA), key distribution  PEM: rigid hierarchy of CAs.  S/MIME: (being agnostic), assume that a number of parallel independent hierarchies.  PGP: anarchy, each user decides which keys to trust. You contact Alice in person to get Alice ’ s public key, and trust it You find the public key of Alice on her web page or from , you can copy it to your PGP system to trust it if you want. Public key server (e.g., paderborn.de/pgp/).

PGP--certificates Certificates are an optional in PGP anyone can issue a certificate to anyone else If you trust Alice and get Carol ’ s public key certificate signed by Alice, you will trust Carol ’ s public key If you get Carol ’ s two public key certificates, one signed by Alice, and the other signed by Bob, both Alice and Bob are trusted by you, then you can trust both Carol ’ s certificates. Therefore PGP is very flexible and easy to use

Security services for Privacy/confidentiality Authentication Integrity Non-repudiation Proof of submission (same as certified mail) Proof of delivery (same as post mail request return receipt) Anonymity Message flow confidentiality Containment Audit Accounting Self destruct Message sequence integrity

Secure (Encode and check sign) Alice:  generates random symmetric private key, K S.  encrypts message with K S (for efficiency)  also encrypts K S with Bob’s public key.  sends both K S (m) and K B (K S ) to Bob.  Alice wants to send confidential , m, to Bob. K S ( ). K B ( ) K S (m ) K B (K S ) + m KSKS KSKS KBKB + Internet K S ( ). K B ( ). - KBKB - KSKS m K S (m ) K B (K S ) +

Secure (Encode and check sign) Bob:  uses his private key to decrypt and recover K S  uses K S to decrypt K S (m) to recover m  Alice wants to send confidential , m, to Bob. K S ( ). K B ( ) K S (m ) K B (K S ) + m KSKS KSKS KBKB + Internet K S ( ). K B ( ). - KBKB - KSKS m K S (m ) K B (K S ) +

Secure (Sign) Alice wants to provide sender authentication message integrity. Alice digitally signs message. sends both message (in the clear) and digital signature. H( ). K A ( ) H(m ) K A (H(m)) - m KAKA - Internet m K A ( ). + KAKA + K A (H(m)) - m H( ). H(m ) compare

Secure (Another Application) Alice wants to provide secrecy, sender authentication, message integrity. Alice uses three keys: her private key, Bob’s public key, newly created symmetric key H( ). K A ( ). - + K A (H(m)) - m KAKA - m K S ( ). K B ( ). + + K B (K S ) + KSKS KBKB + Internet KSKS

PGP overview Not just for , it performs encryption and integrity protection on files  Your is treated as a file  Encrypt the file  Send the encrypted file by regular er.  The receiver saves the to a file and then, decrypt the file by PGP Directly embedded in for convenience. Visit:

Certificate and key revocation You can revoke (delete) any public key anytime A public key of a person can be revoked by the corresponding private key The issuer of a certificate can revoke the certificate  Does not mean that the holder of revoked certificate is a bad person, but the issuers does not want to vouch for its authenticity. Validity period of a key and a certificate

PGP — key ring A data structure containing key materials  pubring.pgp: containing your public keys, other people ’ s public keys, information about people, and certificates.  secring.pgp: containing your private keys. Three trust levels currently in PGP: none, partial, complete. A trust level of a person may determine the trust level of the certificates signed by the person.

Final Demo Show WinPT - Windows Privacy Tools Windows Privacy Tools (WinPT) is a collection of multilingual applications for digital encryption and signing of content. WinPT is GnuPG-based, compatible with OpenPGP compliant software (like PGP) and free for commercial and personal use under the GPL.