We examine the risk to lost, stolen, or unattended smartphones due to attempts to guess the device’s unlock PIN, the most widespread authentication scheme for smartphones. We find novice attacks by those lacking forensic tools or training to be common, with over one-third of survey participants (n = 210) admitting trying to unlock someone’s smartphone without their knowledge in the past year. We further find these novice attacks to be surprisingly effective against PINs, with participants guessing roughly the PIN of 1 in 8 strangers. Our study also produces the first attacking PIN dataset, to our knowledge, obtained from participants guessing PINs of other participants. We additionally investigate participants’ mental models for how and when PIN-guessing may be attempted, finding that most participants expect insiders (friends, family, partners) to be those most likely to attempt to access their smartphone, underestimating risks from strangers due to loss, theft or recycling of their devices.

In this article, we provide the first comprehensive study of user-chosen four- and six-digit PINs ( n =1705) collected on smartphones with participants being explicitly primed for device unlocking. We find that against a throttled attacker (with 10, 30, or 100 guesses, matching the smartphone unlock setting), using six-digit PINs instead of four-digit PINs provides little to no increase in security and surprisingly may even decrease security. We also study the effects of blocklists, where a set of “easy to guess” PINs is disallowed during selection. Two such blocklists are in use today by iOS, for four digits (274 PINs) as well as six digits (2,910 PINs). We extracted both blocklists and compared them with six other blocklists, three for each PIN length. In each case, we had a small (four-digit: 27 PINs; six-digit: 29 PINs), a large (four-digit: 2,740 PINs; six-digit: 291,000 PINs), and a placebo blocklist that always excluded the first-choice PIN. For four-digit PINs, we find that the relatively small blocklist in use today by iOS offers little to no benefit against a throttled guessing attack. Security gains are only observed when the blocklist is much larger. In the six-digit case, we were able to reach a similar security level with a smaller blocklist. As the user frustration increases with the blocklists size, developers should employ a blocklist that is as small as possible while ensuring the desired security. Based on our analysis, we recommend that for four-digit PINs a blocklist should contain the 1,000 most popular PINs to provide the best balance between usability and security and for six-digit PINs the 2,000 most popular PINs should be blocked.

We conducted an online study with $n = 235$ Signal users on their understanding and usage of PINs in Signal. In our study, we observe a split in PIN management and composition strategies between users who can explain the purpose of the Signal PINs (56%; enthusiasts) and users who cannot (44%; casual users). Encouraging adoption of PINs by Signal appears quite successful: only 14% opted-out of setting a PIN entirely. Among those who did set a PIN, most enthusiasts had long, complex alphanumeric PINs generated by and saved in a password manager. Meanwhile more casual Signal users mostly relied on short numeric-only PINs. Our results suggest that better communication about the purpose of the Signal PIN could help more casual users understand the features PINs enable (such as that it is not simply a personal identification number). This communication could encourage a stronger security posture.

In this paper, we provide the first comprehensive study of user-chosen 4- and 6-digit PINs (n = 1220) collected on smartphones with participants being explicitly primed for device unlocking. We find that against a throttled attacker (with 10, 30, or 100 guesses, matching the smartphone unlock setting), using 6-digit PINs instead of 4-digit PINs provides little to no increase in security, and surprisingly may even decrease security. We also study the effects of blacklists, where a set of "easy to guess" PINs is disallowed during selection. Two such blacklists are in use today by iOS, for 4-digits (274 PINs) as well as 6-digits (2910 PINs). We extracted both blacklists compared them with four other blacklists, including a small 4-digit (27 PINs), a large 4-digit (2740 PINs), and two placebo blacklists for 4- and 6-digit PINs that always excluded the first-choice PIN. We find that relatively small blacklists in use today by iOS offer little or no benefit against a throttled guessing attack. Security gains are only observed when the blacklists are much larger, which in turn comes at the cost of increased user frustration. Our analysis suggests that a blacklist at about 10% of the PIN space may provide the best balance between usability and security.

Augmented-reality glasses like Google Glass present a new set of user-interface trade-offs which must be carefully considered in crafting user authentication protocols. First, it lacks a keyboard or touchscreen; second, the most prominent input mechanisms, voice recognition and a swipe sensor, are both easily observable by bystanders and thus are not suitable for password entry. Fortunately, these devices offer a private display that cannot easily be viewed by bystanders, and which helps in constructing secure user authentication. In this position paper we will outline problems and possible solutions for authentication on augmented-reality glasses.

Multiple studies have demonstrated that users select weak passwords. However, the vast majority of studies on password security uses password lists that only have passwords for one site, which means that several important questions cannot be studied. For example, how much stronger are password choices for different categories of sites? We use a dataset which we extracted from a large dump of malware records. It contains multiple accounts (and passwords) per user and thus allows us to study both password re-use and the correlation between the value of an account and the strength of the passwords for those accounts. The first contribution of our study shows that users in our sample choose (substantially) stronger passwords for financial accounts than for low-value accounts, based on the extracted passwords as well as publicly available lists. This contribution has implications for password research, as some widely-used lists contain passwords much weaker than those used in the real world (for accounts of more than low value). In our second contribution, we measure password re-use taking account values into account. We see that although high-value passwords are stronger, they are re-used more frequently than low-value passwords – valuable passwords are identical to 21

This memo describes the use of the Advanced Encryption Standard (AES) in the Counter and CBC-MAC Mode (CCM) of operation within Transport Layer Security (TLS) to provide confidentiality and data-origin authentication.The AES-CCM algorithm is amenable to compact implementations, making it suitable for constrained environments, while at the same time providing a high level of security.The cipher suites defined in this document use Elliptic Curve Cryptography (ECC) and are advantageous in networks with limited bandwidth.