Restrictions

• The exponent of the RSA public key must be odd.
• The command PKA Decrypt - Disallow PKOAEP2 (offset X'03F2') is not available in releases before Release 8.1.

When using the PKOAEP2 recovery method, the following restrictions apply:

• the OAEP standard (PKCS #1) defines overhead = (2 * hLen) + 2 bytes. Parameter hLen is the encoding hash algorithm output length in bytes. This gives additional overhead:
  • 42 Bytes for SHA-1
  • 58 Bytes for SHA-224
  • 66 Bytes for SHA-256
  • 98 Bytes for SHA-384
  • 130 Bytes for SHA-512
• RSA key size restrictions:
  • The RSA key used must have a modulus size greater than or equal to the total PKOAEP2 message bit length, calculated with the data previously shown, as: source data size + total overhead
  • The minimum source data length is zero bytes, giving total message sizes (and therefore minimum RSA key sizes):
    • 0 + 42 = 42 Bytes (336 bits) for SHA-1 OAEP
    • 0 + 58 = 58 Bytes (464 bits) for SHA-224 OAEP
    • 0 + 66 = 66 Bytes (528 bits) for SHA-256 OAEP
    • 0 + 98 = 98 Bytes (784 bits) for SHA-384 OAEP
    • 0 + 130 = 130 Bytes (1040 bits) for SHA-512 OAEP
  • The maximum RSA key size is 8192 bits (1024 bytes), therefore the maximum message size is key size - overhead:
    • 1024 – 42 = 982 Bytes (7856 bits) for SHA-1 OAEP
    • 1024 – 58 = 966 Bytes (7728 bits) for SHA-224 OAEP
    • 1024 – 66 = 958 Bytes (7664 bits) for SHA-256 OAEP
    • 1024 – 98 = 926 Bytes (7856 bits) for SHA-384 OAEP
    • 1024 – 130 = 894 Bytes (3056 bits) for SHA-512 OAEP