PGP (Pretty Good Privacy) is an open source encryption software that provides security mechanisms like authentication, confidentiality, compression, and email compatibility. It uses strong cryptographic algorithms like IDEA, RSA, and SHA-1. PGP protects messages by signing them with the sender's private key, encrypting them with a random symmetric key, and encrypting that key with the recipient's public key. This ensures message integrity and confidentiality. Compression is applied before encryption to save space. Radix-64 encoding allows encrypted messages to be transmitted over email. PGP's features help secure email communications and stored files from unauthorized access.

1. PRETTY GOOD PRIVACY
from CNS
Presented by,
Punnya sureshbabu

2. PGP
• PGP was invented by Phil Zimmermann.
• Used to provide Email with privacy.
• It is an open source.
• ƒBased on strong cryptographic algorithms (IDEA, RSA, SHA-1).

3. Scenarios
• Plaintext
• Message integrity
• Compression
• Confidentiality with one-time session key
• Code conversion
• Segmentation

4. Plaintext
• Simplest scenario.
• There is no message integrity.
• Sender compose the message and send it to the receiver.
• The message stored in receivers mailbox, until it is received by
him.

5. Message integrity
• Sender create a message and ends with her private
key.
• When receiver receives the message, he get the
message by using senders public key.
Compression
• Compress the message.
• No security benefits.
• Easy to send.

6. Confidentiality with one-time session key
• First sender create session key.
• Using this session key , sender encrypt the message.
• Then send the message with the key to the receiver.
• Receiver receive the package.
• He encrypt the session key using his private key.
• Receiver use the session key to encrypt the message.
• After decrypt the message, receiver create a digest of the
message and check.
• If both are equal, then the message is authentic.

7. Code conversion
• Most email message consist of ASCII characters.
• To translate the characters PGP uses Radix-64
conversion.
Segmentation
• Maximum message length restrictions in email.
• PGP automatically subdivides a large message into
segments small enough to mail separately.

8. Services provide by PGP
• Authentication
• Confidentiality
• Compression
• E-mail compatibility

9. Authentication
• The sender creates a message.
• SHA-1 is used to generate a 160-bit hash code of the message.
• The hash code is encrypted with RSA using the sender’s
private key, and the result is pretended to the message.
• The receiver uses RSA with the sender’s public key to decrypt
and recover the hash code.
• The receiver generates a new hash code for the message and
compares it with the decrypted hash code. If the two match,
the message is accepted as authentic.

11. Confidentiality
• PGP another service is confidentiality, which is encrypting
messages for transmitting or to store files locally.
• In both cases, the symmetric encryption algorithm CAST-128
may be used. Alternatively, IDEA or 3DES may be used. And
the 64-bit cipher feedback (CFB) mode is used.
• In PGP, each symmetric key is used only once. The session
key is bound to the message. To protect the key, it is encrypted
with the receiver’s public key.

12. • The sender generates a message and a random 128-bit number
to be used as a session key for this message only.
• The message is encrypted using CAST-128 (or IDEA or
3DES) with the session key.
• The session key is encrypted with RSA using the recipient’s
public key and is prepended to the message.
• The receiver uses RSA with its private key to decrypt and
recover the session key. 5. The session key is used to decrypt
the message.

14. Notations
EP – Public key encryption(use either public key of receiver or private
key of sender)
DP – Public key decryption(we have to check for the encryption
process which key is used at the encryption so the other key should
be used in the decryption.
EC – conventional encryption.(symmetric encryption same key used by
ender and receiver)
DC – Conventional decryption.
H – Hash function/ hash code
Z – zip (compression)
KS – secret key used in conventional encryption.

15. Combine Authentication &
Confidentiality
• First, a signature is generated for the plaintext message and
prepended to the message. Then the plaintext message plus
signature is encrypted using CAST-128 (or IDEA or 3DES),
and the session key is encrypted using RSA (or ElGamal).
• In summary, when both services are used, the sender first
signs the message with its own private key, then encrypts the
message with a session key, and finally encrypts the session
key with the recipient’s public key.

17. • FOR ACHIEVING AUTHENTICATION
DSS approach with SHA alg
or
RSA with SHA alg
• FOR ACHIEVING THE CONFIDENTIALITY
CAST/IDEA/TRIPLE DES with DIFFIE HELLMAN KEY EXCHANGE

18. Compression
• PGP compresses the message after applying the signature but before
encryption. This has the benefit of saving space both for e-mail
transmission and for file storage.
• Z for compression and Z–1 for decompression The signature is generated
before compression for two reasons:
• It is preferable to sign an uncompressed message so that one can store only
the uncompressed message together with the signature for future
verification.
• If you generate signature after compression then there is a need
recompression for message verification, PGP’s compression algorithm
presents a difficulty.
• Message encryption is applied after compression to strengthen
cryptographic security. Therefore cryptanalysis is more difficult.
• The compression algorithm used here is ZIP Algorithm

19. E-mail compatibility
• The resulting message block consists of a stream of arbitrary 8-bit octets.
• However, many electronic mail systems only permit the use of blocks
consisting of ASCII text.
• To accommodate this restriction, PGP provides the service of converting
the raw 8-bit binary stream to a stream of printable ASCII characters.
• The scheme used for this purpose is radix-64 conversion. Each group of
three octets of binary data is mapped into four ASCII characters. This
format also appends a CRC to detect transmission errors.
• The use of radix 64 expands a message by 33%. Fortunately, the session
key and signature portions of the message are relatively compact, and the
plaintext message has been compressed.
• In fact, the compression should be more than enough to compensate for the
radix-64 expansion.

21. ADVANTAGES OF PGP
• Your valuable information is always protected, others cannot
view it, and it cannot be stolen over the Internet .
• No compatibility problems - works with any email application
that you or your recipients are using .
• Verification of the sender of information ensures you are not
being spoofed by a third party.
• Absolute assurity that the information you send or receive has
not been modified in transit.
• Your secure mail and text cannot be infiltrated by hackers or
infected and mis-used by email attacks

22. DISADVANTAGES OF PGP
• Administering conflicting versions.
• Compatibility issues.
• Complexity.
• No recovery.

23. Thankyou