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Asked: 2026-05-28T20:14:13+00:00

what is meant by security strength of a random number when using Hash_DRBG? (I

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what is meant by security strength of a random number when using Hash_DRBG? (I am referring to some NIST documents).

The document for Hash_DRBG says:
“Requested Security Strength = 80
Requested Hash Algorithm = SHA-1”

[ I have edited the title . I think my question is more accurate now ]

The document is http://csrc.nist.gov/groups/ST/toolkit/documents/Examples/DRBG_All.pdf
(It is around 11MB)

The relevant section is

##############################################################
Hash_DRBG
Requested Security Strength = 80
Requested Hash Algorithm = SHA-1
prediction_resistance_flag = "NOT ENABLED"
EntropyInput =
000102 03040506
0708090A 0B0C0D0E 0F101112 13141516 1718191A 1B1C1D1E
1F202122 23242526 2728292A 2B2C2D2E 2F303132 33343536
EntropyInput1 (for Reseed1) =
808182 83848586
8788898A 8B8C8D8E 8F909192 93949596 9798999A 9B9C9D9E
9FA0A1A2 A3A4A5A6 A7A8A9AA ABACADAE AFB0B1B2 B3B4B5B6
EntropyInput2 (for Reseed2) =
C0C1C2 C3C4C5C6
C7C8C9CA CBCCCDCE CFD0D1D2 D3D4D5D6 D7D8D9DA DBDCDDDE
DFE0E1E2 E3E4E5E6 E7E8E9EA EBECEDEE EFF0F1F2 F3F4F5F6
Nonce =
20 21222324
PersonalizationString = <empty>
AdditionalInput = <empty>
##############################################################
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1 Answer

  1. Editorial Team

    Security strength of a hash algorithm is the difficulty of reversing hashed data.

    In the NIST Special Publication 800-107 (PDF), the strength of a cryptographic algorithm is

    A number associated with the amount of work (that is, the number of
    operations) that is required to break a cryptographic algorithm or
    system. Security strength is measured in bits. If 2N execution
    operations of the algorithm (or system) are required to break the
    cryptographic algorithm, then the security strength is N bits.

    And the security strength of a secret key is

    The required amount of work to find the key that is associated with
    some specific algorithm.

    And also

    The security strength of a cryptographic hash function is determined
    by either: its collision resistance strength, preimage resistance
    strength or second preimage resistance strength, depending on the
    property(ies) that the cryptographic application needs from the
    cryptographic hash function.

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