What are Digital Signatures?

Digital signatures allow a person to sign a digital object in much the same way they would apply a signature to paper and with the assurance that the signature cannot be forged and neither the document or the signature can be modified without making the signature invalid.

Under what circumstances are Digital Signatures required?

A valid digital signature gives a recipient of an object reason to believe that the object was created by a known sender, that the sender cannot deny having sent the object and that the object was not altered in transit. Digital signatures are commonly used for IT transactions where it is important to detect forgery or tampering. For example, they can be used by clinical staff to sign electronic health records (much as they would physically sign a paper-based record).

How are Digital Signatures achieved?

A digital signature scheme typically consists of three algorithms:

  • key generation algorithm that selects a private key uniformly at random from a set of possible private keys. The algorithm outputs the private key and a corresponding public key.
  • signing algorithm that, given a message and a private key, produces a signature.
  • signature verifying algorithm that, given the message, public key and signature, either accepts or rejects the message’s claim to authenticity.

National Digital Signature Frameworks

eSignature v1.0

eSignature v1.0 is an electronic signatures recommendations document that explores the legal context for electronic signatures on clinical documents (Prescriptions, Dispense Records, Referrals, Specialist Letters, Diagnostic Imaging Requests and Reports, Discharge Summaries), explains key concepts relating to electronic signatures, and analyses the clinical and business risks associated with the signer’s identity in order to draw conclusions about the most appropriate signature mechanisms to use on different types of clinical documents.

It has been developed by the National E-Health Transition Authority (NEHTA) and refers extensively to NEHTA’s National Authentication Service for Health (NASH) Public Key Infrastructure (PKI).

The applicability of digital signatures as a requirement in the Health and Medical research requires ongoing examination.

What are the Australian Standards for Digital Signatures?

The Australian Signals Directorate (ASD) provides extensive guidance to Commonwealth entities surrounding standards to safeguard data ranging in different levels of sensitivity, from “unclassified but sensitive or official information not intended for public release” (UD), through “protected” (P), to “Top Secret” (TS). Associated security controls are outlined in the ASD’s Information Security Manual (ISM).

Whilst it is only Australian Government agencies that are required to adopt the ASD controls outlined in the ISM, the controls also provide a useful framework for non-government organisations to consider when protecting data that ranges across various levels of sensitivity. Data of this type includes Personal Health Information that contains identifying aspects which is considered to be both “sensitive”[1] and “protected”[2].

The following ASD controls are issued for agencies in protecting data that are considered “unclassified but sensitive or official information not intended for public release” (UD) or “protected” (P).

ASD Approved Cryptographic Algorithms (AACA)

The ASD approved asymmetric/public key algorithms for digital signatures are:

  • Digital Signature Algorithm (DSA)
  • Elliptic Curve Digital Signature Algorithm (ECDSA)
  • Rivest–Shamir–Adleman (RSA)

Digital Signature Controls

ASD Control: 0473; Revision: 3 states that agencies using DSA for the approved use of digital signatures must use a modulus of at least 1024 bits.

ASD Control: 0475; Revision: 3 states that agencies using ECDSA for the approved use of digital signatures must use a field/key size of at least 160 bits.

ASD Control: 0476; Revision: 4 states that agencies using RSA, both for the approved use of digital signatures and passing encryption session keys or similar keys, must use a modulus of at least 1024 bits.

ASD Control: 0477; Revision: 5 states that agencies using RSA, both for the approved use of digital signatures and for passing encryption session keys or similar keys, must ensure that the key pair used for passing encrypted session keys is different from the key pair used for digital signatures.

Data Integrity Checks

ASD Control: 1292; Revision: 0 states that agencies should verify the integrity of content where applicable, and block the content if verification fails.

[1] The Commonwealth Privacy Act (1988) defines what is considered personal and sensitive information in Australia. Personal Information means information about an identified individual, or an individual who is reasonably identifiable, and of relevance to, Sensitive Information includes: Information about an individual’s Racial or ethnic origin or Sexual orientation or practices; Health information; Genetic information and Biometric information.
[2] The US HIPPA Privacy Rule ( ) defines protected health information” as individually identifiable health information, including identifiable demographic and other information relating to the past, present, or future physical or mental health or condition of an individual, or the provision or payment of health care to an individual that is created or received by a health care provider, health plan, employer, or health care clearinghouse. Genetic information is considered to be health information.