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rpm
4.18.0
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5.7. More...
#include <rpmpgp.h>
Data Fields | |
| uint8_t | data [1] |
5.7.
Symmetrically Encrypted Data Packet (Tag 9)
The Symmetrically Encrypted Data packet contains data encrypted with a symmetric-key algorithm. When it has been decrypted, it will typically contain other packets (often literal data packets or compressed data packets).
The body of this packet consists of:
The symmetric cipher used may be specified in an Public-Key or Symmetric-Key Encrypted Session Key packet that precedes the Symmetrically Encrypted Data Packet. In that case, the cipher algorithm octet is prefixed to the session key before it is encrypted. If no packets of these types precede the encrypted data, the IDEA algorithm is used with the session key calculated as the MD5 hash of the passphrase.
The data is encrypted in CFB mode, with a CFB shift size equal to the cipher's block size. The Initial Vector (IV) is specified as all zeros. Instead of using an IV, OpenPGP prefixes a 10-octet string to the data before it is encrypted. The first eight octets are random, and the 9th and 10th octets are copies of the 7th and 8th octets, respectively. After encrypting the first 10 octets, the CFB state is resynchronized if the cipher block size is 8 octets or less. The last 8 octets of ciphertext are passed through the cipher and the block boundary is reset.
The repetition of 16 bits in the 80 bits of random data prefixed to the message allows the receiver to immediately check whether the session key is incorrect.
1.9.1