R v. CB, 2019 ONCA 380 (Watt):

[63] To determine this ground of appeal requires consideration of what is involved in the process of authentication; how it may be established, especially with respect to the subject-matter in issue here; and the roles of the trier of law and the trier of fact in the authentication process.

[64] The requirement of authentication applies to various kinds of real evidence. Authentication involves a showing by the proponent of the evidence that the thing or item proffered really is what its proponent claims it to be: Kenneth S. Broun, ed., McCormick on Evidence, 7th ed., vol. 2 (Thomson Reuters, 2013), at $S 212, pp. 4-5.

[65] Authentication is the process of convincing a court that a thing matches the claim made R. v. C.B., [2019] O.J. No. 2425 about it. In other words, it is what its proponent claims it to be. Authentication is intertwined with relevance: in the absence of authentication, the thing lacks relevance unless it is tendered as bogus. Thus, authentication becomes necessary where the item is tendered as real or documentary evidence.

[66] At common law, authentication requires the introduction of some evidence that the item is what it purports to be: R. v. Donald (1958), 121 C.C.C. 304 (N.B.C.A., at p. 306; R. v. Staniforth (1979), 11 C.R. (3d) 84 (Ont. C.A.), at p. 89; R. v. Hirsch, 2017 SKCA 14, 353 C.C.C. (3d) 230, at para. 18. The requirement is not onerous and may be established by either or both direct and circumstantial evidence.

[67] For electronic documents, s. 31.1 of the CEA assigns a party who seeks to admit an electronic document as evidence the burden of proving its authenticity. To meet this burden, the party must adduce evidence capable of supporting a finding that the electronic document is what it purports to be. Section 31.8 provides an expansive definition of “electronic document”, a term which encompasses devices by or in which data is recorded or stored. Under s. 31.1, as at common law, the threshold to be met is low. When that threshold is satisfied, the electronic document is admissible, and thus available for use by the trier of fact.

[68] To satisfy this modest threshold for authentication, whether at common law or under s. 31.1 of the CEA, the proponent may adduce and rely upon direct and circumstantial evidence. Section 31.1 does not limit how or by what means the threshold may be met. Its only requirement is that the evidence be capable of supporting a finding that the electronic document “is that which it is purported to be.” That circumstantial evidence may be relied upon is well established: Hirsch, at para. 18; R. v. Colosie, 2016 ONSC 1708, at para. 25; R. v. Bulldog, 2015 ABCA 251, 326 C.C.C (3d) 385, at para. 35; see also R. v. Evans, [1993] 3 S.C.R. 653, at p. 663. This accords with general principles about proof of facts in criminal proceedings, whether the facts sought to be established are preliminary facts on an admissibility inquiry or ultimate facts necessary to prove guilt.

[69] At common law, correspondence could be authenticated by the “reply letter” doctrine: to authenticate correspondence as having been sent by one individual to another, evidence is adduced to show it is a reply to a letter sent to that person. As a matter of logic, the same should hold true for text messages and emails. Evidence that A sent a text or email to B whom A believed was linked to a specific address, and evidence of a response purportedly from B affords some evidence of authenticity: David Paciocco, “Proof and Progress: Coping with the Law of Evidence in a Technological Age” (2013) 11 C.J.L.T. 181, at pp. 197-8 (Paciocco).

[70] In a similar way, text messages may be linked to particular phones by examining the recorded number of the sender and receiving evidence linking that number to a specific individual, as for example, by admission: Paciocco, at p. 198.

[71] But what of the prospect of tampering? Does it have to be negated before digital evidence can be properly authenticated?

[72] As a matter of principle, it seems reasonable to infer that the sender has authored a message sent from his or her phone number. This inference is available and should be drawn in the absence of evidence that gives an air of reality to a claim that this may not be so. Rank speculation is not sufficient: R. v. Ambrose, 2015 ONCJ 813, at para. 52. And even if there were an air of reality to such a claim, the low threshold for authentication, whether at common law or R. v. C.B., [2019] O.J. No. 2425 under s. 31.1 of the CEA, would seem to assign such a prospect to an assessment of weight.