6 ms·

As uuid v7 hold time information, they can help bad actors for timing attacks or pattern recognition because they contain a time information linked to the recor

As uuid v7 hold time information, they can help bad actors for timing attacks or pattern recognition because they contain a time information linked to the record. You can guess the time the system took between 2 uuid v7 id's. They can only be used if they're not shown to the user. (so not in the form mysite.com/mypage? id=0190854d-7f9f-78fc-b9bc-598867ebf39a) A big serial starting at a high number can't provide the time information.

TeeWEE 2y ago
Big serial is sequential and it’s very easy to guess the next number. So you got the problem of sequential key attack… If you use only uuid in your outwards facing api then you still have the problem of slow queries. Since you need them to find the object (as mentioned below) UUIDv7 has a random part, can be created distributedly, and indexes well. It’s the best choice for modern application that support distributed data creation.
- badestrand 2y ago
  You never expose the bigserial, you generate a ID (like UUID) for external use/identification and simply have an index over that column for fast selects.
  - stoperaticless 2y ago
    Amen (or similar)
  - kroolik 2y ago
    Having an index over the uuid is equivalent to it being a PK, so why would you bother having both?
    - blackenedgem 2y ago
      Because it's much better for range queries and joins. When you inevitably need to take a snapshot of the table or migrate the schema somehow you'll be wishing you had something else other than a UUID as the PK.
      - groestl 2y ago
        Ha? Please elaborate.
        kroolik 2y ago
        When running a batched migration it is important to batch using a strictly monotonic field so that new rows wont get inserted in already processed range
        asah 2y ago
        would creation/lastmod timestamps cover this requirement?
        deleted 2y ago
        [deleted]
        kroolik 2y ago
        Yes, although timestamps may have collisions depending on resolution and traffic, no? Bigserials (at least in PG), are strictly monotonic (with holes).
        blackenedgem 2y ago
        It's not even necessarily it being strictly monotonic. That part does help though as you don't need to skip rows. For me the bigger thing is the randomness. A uid being random for a given row means the opposite is true; any given index entry points to a completely random heap entry. When backfilling this leads to massive write amplification. Consider a table with rows taking up 40 bytes, so roughly 200 entries per page. If I backfill 1k rows sorted by the id then under normal circumstances I'd expect to update 6-7 pages which is ~50kiB of heap writes. Whereas if I do that sort of backfill with a uid then I'd expect to encounter each page on a separate row. That means 1k rows backfilled is going to be around 8MB of writes to the heap.
        valenterry 2y ago
  - iterateoften 2y ago
    If you have an index on the uuid anyways having a separate big serial field for PK doesn’t help that much.
    - rezonant 2y ago
      As mentioned elsewhere, it ensures the ability to perform resumable and consistent batching queries across the data set without missing records. Ordering over an insertion timestamp is not enough if two records may have the same timestamp: You may miss a record (or visit a record twice) across multiple queries.
      - disneycember 2y ago
        This is solved sorting by timestamp first then by random PK UUID. Don't think a little simpler batch queries justify leaking time and quantity information or complexity of handling two types of IDs.
        j45 2y ago
        I agree with not baking more intelligence into a piece of data than needed, especially an index.
        rezonant 2y ago
        You wouldn't expose the numeric IDs publically, and ideally you'd use your database's automatic ID selection to avoid any complexity. The UUID sorting works in the common case, but if you happen to end your batch near the current time, you still run the risk of losing a few records if the insert frequency is sufficiently high. Admittedly this is only a problem when you are batching through all the way to current insertions.
- j45 2y ago
  Sequential numbers can not be used publicly. Also, security can be built around not allowing querying records which are not yours. I'm all for a little security through obscurity including UUIDs but it shouldn't be the sole thing. Easier to generate a UUID for the sequential and let the database do what it does best (relate many serials among each other). The other part is being able to use what's built into the database out of the box without a lot more configuration. Selfishly, I always appreciate learning more about Postgres though :)
arp242 2y ago
For almost all use cases just showing a UUIDv7 or sequential ID is fine. There are a few exceptions, but it's not the common case.
- mewpmewp2 2y ago
  How would it be fine, e.g. for e commerce which is arguably very large portion of the use cases? You would be immediately leaking how many orders a day your business is getting with sequential id.
  - arp242 2y ago
    > You would be immediately leaking how many orders a day your business is getting with sequential id. Which is fine for almost all of them. All brick and mortar stores "leak" this too; it's really not that hard to guess number of orders for most businesses, and it's not really a problem for the overwhelming majority. And "Hi, this is Martin, I'd like to ask a question about order 2bf8aa01-6f4e-42ae-8635-9648f70a9a05" doesn't really work. Neither does "John, did you already pay order 2bf8aa01-6f4e-42ae-8635-9648f70a9a05" or "Alice, isn't 2bf8aa01-6f4e-42ae-8635-9648f70a9a05 the same as what we ordered with 7bb027c3-83ea-481a-bb1e-861be18d21ea?" Especially for order IDs UUIDs are huge PITA because unlike user IDs and other more "internal" IDs, people can and do want to talk about them. You will need some secondary human-friendly unique ID regardless (possibly obfuscated, if you really want to), and if you have that, then why bother giving UUIDs to people?
    - badestrand 2y ago
      Best solution is to have a serial identifier internally and a generated ID for external. And yes it shouldn't be a UUID as they are user-hostile, it should be something like 6-10 letters+digits.
  - inopinatus 2y ago
    There are jurisdictions e.g. Germany in which a consecutive sequence for invoice numbers is a mandatory, legislated requirement (mercifully, gaps are generally permitted, with caveats) For extra spice, in some places this is legislated as a per-seller sequence, and in others as a per-customer sequence, so there’s no policy you can apply globally, and this once again highlights the separation of concerns between a primary key and a record locator/identifier.
sebazzz 2y ago
> As uuid v7 hold time information, they can help bad actors for timing attacks or pattern recognition because they contain a time information linked to the record. Are you then not doing security by randomness if that is the thing that worries you?
OskarS 2y ago
Can I ask (as a humble application developer, not a backend/database person), if the two requirements are: 1. The UUIDs should be ordered internally, for B-tree performance 2. The UUIDs should not be ordered externally, for security reasons Why not use encryption? The unencrypted ID is a sequential id, but as soon as it leaves the database, it's always encrypted. Like, when getting it out: SELECT encrypt(id) FROM table WHERE something = whatever; and when putting stuff in: UPDATE table SET something = whatever WHERE id = decrypt(<encrypted-key>) Seems like the best of both worlds, and you don't need to store separate things.
- spencerap 2y ago
  If the key and encryption mechanism are ever leaked, those opaque external IDs can be converted easily back to sequence numbers, and vice versa, which might pose a risk for you or your users. You won't be able to rotate the encryption key without breaking anything external that tracks those encrypted IDs... third party services, SEO, user bookmarks, etc.
  - OskarS 2y ago
    You store the key in the database, right? Like, if the database leaks, it doesn’t matter if your ids are sequeneced or unsequenced, because all data has leaked anyway. The key leaking doesn’t seem like a realistic security issue.
    - zxexz 2y ago
      Ideally if you do this, you store the key in a separate schema with proper roles so that you can call encrypt() with the database role, which can't select the key. Even then, the decrypted metadata should not be particularly sensitive - and should immutably reference a point in time so you can validate against some known key revocation retroactively. My take is it's rarely necessary to have a token, that you give to an external entity, that has any embedded metadata all - 99.9% of apps aren't operating at a scale where even a million-key hashmap sitting in ram and syncing changes to disk on update would cause any performance difference.
thiht 2y ago
I don’t understand how that’s an issue. Do you have an example of a possible attack using UUIDv7 timestamp? Is there evidence of this being a real security flaw?
- cqqxo4zV46cp 2y ago
  I don’t understand this thinking. If you understand what’s at play, you can infer the potential security implications. What you’re advocating for is being entirely reactive instead of also being proactive.
  - thiht 2y ago
    No, I don’t. Even with a timestamp uuids are not enumerable, and honestly I don’t care that the timestamp they were created at is public. Is the version of uuid used being a part of the uuid considered a leak too?
- whynotmaybe 2y ago
  The draft spec for uuid v7 has details about the security considerations : https://www.ietf.org/archive/id/draft-peabody-dispatch-new-uuid-format-01.html#name-security-considerations https://www.ietf.org/archive/id/draft-peabody-dispatch-new-u... The way I see it is that uuid v7 in itself is great for some use but not for all uses. You always have to remember that a v7 always carries the id's creation time as metadata with it, whether you want it or not. And if you let external users get the v7, they can get that metadata. I'm not a security expert but I know enough to know that you should only give the minimal data to a user. My only guess is that v7 being so new, attacks aren't widespread for now, and I know why the author decided not to focus on "if UUID is the right format for a key", because the answer is no 99% of the time.
  - thiht 2y ago
    That just seems overly cautious. I’d rather use UUIDv7 unless I have a reason not to. The convenience of sortable ids and increased index locality are very much worth the security issues associated with UUIDv7. Maybe I wouldn’t use UUIDv7 for tokens or stuff like that, but DB IDs seem pretty safe.

TeeWEE 2y ago

Big serial is sequential and it’s very easy to guess the next number. So you got the problem of sequential key attack… If you use only uuid in your outwards facing api then you still have the problem of slow queries. Since you need them to find the object (as mentioned below) UUIDv7 has a random part, can be created distributedly, and indexes well. It’s the best choice for modern application that support distributed data creation.

badestrand 2y ago
You never expose the bigserial, you generate a ID (like UUID) for external use/identification and simply have an index over that column for fast selects.
- stoperaticless 2y ago
  Amen (or similar)
- kroolik 2y ago
  Having an index over the uuid is equivalent to it being a PK, so why would you bother having both?
  - blackenedgem 2y ago
    Because it's much better for range queries and joins. When you inevitably need to take a snapshot of the table or migrate the schema somehow you'll be wishing you had something else other than a UUID as the PK.
    - groestl 2y ago
      Ha? Please elaborate.
      - kroolik 2y ago
        When running a batched migration it is important to batch using a strictly monotonic field so that new rows wont get inserted in already processed range
        asah 2y ago
        would creation/lastmod timestamps cover this requirement?
        deleted 2y ago
        [deleted]
        kroolik 2y ago
        Yes, although timestamps may have collisions depending on resolution and traffic, no? Bigserials (at least in PG), are strictly monotonic (with holes).
        blackenedgem 2y ago
        It's not even necessarily it being strictly monotonic. That part does help though as you don't need to skip rows. For me the bigger thing is the randomness. A uid being random for a given row means the opposite is true; any given index entry points to a completely random heap entry. When backfilling this leads to massive write amplification. Consider a table with rows taking up 40 bytes, so roughly 200 entries per page. If I backfill 1k rows sorted by the id then under normal circumstances I'd expect to update 6-7 pages which is ~50kiB of heap writes. Whereas if I do that sort of backfill with a uid then I'd expect to encounter each page on a separate row. That means 1k rows backfilled is going to be around 8MB of writes to the heap.
        valenterry 2y ago
- iterateoften 2y ago
  If you have an index on the uuid anyways having a separate big serial field for PK doesn’t help that much.
  - rezonant 2y ago
    As mentioned elsewhere, it ensures the ability to perform resumable and consistent batching queries across the data set without missing records. Ordering over an insertion timestamp is not enough if two records may have the same timestamp: You may miss a record (or visit a record twice) across multiple queries.
    - disneycember 2y ago
      This is solved sorting by timestamp first then by random PK UUID. Don't think a little simpler batch queries justify leaking time and quantity information or complexity of handling two types of IDs.
      - j45 2y ago
        I agree with not baking more intelligence into a piece of data than needed, especially an index.
      - rezonant 2y ago
        You wouldn't expose the numeric IDs publically, and ideally you'd use your database's automatic ID selection to avoid any complexity. The UUID sorting works in the common case, but if you happen to end your batch near the current time, you still run the risk of losing a few records if the insert frequency is sufficiently high. Admittedly this is only a problem when you are batching through all the way to current insertions.
j45 2y ago
Sequential numbers can not be used publicly. Also, security can be built around not allowing querying records which are not yours. I'm all for a little security through obscurity including UUIDs but it shouldn't be the sole thing. Easier to generate a UUID for the sequential and let the database do what it does best (relate many serials among each other). The other part is being able to use what's built into the database out of the box without a lot more configuration. Selfishly, I always appreciate learning more about Postgres though :)

arp242 2y ago

For almost all use cases just showing a UUIDv7 or sequential ID is fine. There are a few exceptions, but it's not the common case.

mewpmewp2 2y ago
How would it be fine, e.g. for e commerce which is arguably very large portion of the use cases? You would be immediately leaking how many orders a day your business is getting with sequential id.
- arp242 2y ago
  > You would be immediately leaking how many orders a day your business is getting with sequential id. Which is fine for almost all of them. All brick and mortar stores "leak" this too; it's really not that hard to guess number of orders for most businesses, and it's not really a problem for the overwhelming majority. And "Hi, this is Martin, I'd like to ask a question about order 2bf8aa01-6f4e-42ae-8635-9648f70a9a05" doesn't really work. Neither does "John, did you already pay order 2bf8aa01-6f4e-42ae-8635-9648f70a9a05" or "Alice, isn't 2bf8aa01-6f4e-42ae-8635-9648f70a9a05 the same as what we ordered with 7bb027c3-83ea-481a-bb1e-861be18d21ea?" Especially for order IDs UUIDs are huge PITA because unlike user IDs and other more "internal" IDs, people can and do want to talk about them. You will need some secondary human-friendly unique ID regardless (possibly obfuscated, if you really want to), and if you have that, then why bother giving UUIDs to people?
  - badestrand 2y ago
    Best solution is to have a serial identifier internally and a generated ID for external. And yes it shouldn't be a UUID as they are user-hostile, it should be something like 6-10 letters+digits.
- inopinatus 2y ago
  There are jurisdictions e.g. Germany in which a consecutive sequence for invoice numbers is a mandatory, legislated requirement (mercifully, gaps are generally permitted, with caveats) For extra spice, in some places this is legislated as a per-seller sequence, and in others as a per-customer sequence, so there’s no policy you can apply globally, and this once again highlights the separation of concerns between a primary key and a record locator/identifier.

sebazzz 2y ago

> As uuid v7 hold time information, they can help bad actors for timing attacks or pattern recognition because they contain a time information linked to the record. Are you then not doing security by randomness if that is the thing that worries you?

OskarS 2y ago

Can I ask (as a humble application developer, not a backend/database person), if the two requirements are: 1. The UUIDs should be ordered internally, for B-tree performance 2. The UUIDs should not be ordered externally, for security reasons Why not use encryption? The unencrypted ID is a sequential id, but as soon as it leaves the database, it's always encrypted. Like, when getting it out: SELECT encrypt(id) FROM table WHERE something = whatever; and when putting stuff in: UPDATE table SET something = whatever WHERE id = decrypt(<encrypted-key>) Seems like the best of both worlds, and you don't need to store separate things.

spencerap 2y ago
If the key and encryption mechanism are ever leaked, those opaque external IDs can be converted easily back to sequence numbers, and vice versa, which might pose a risk for you or your users. You won't be able to rotate the encryption key without breaking anything external that tracks those encrypted IDs... third party services, SEO, user bookmarks, etc.
- OskarS 2y ago
  You store the key in the database, right? Like, if the database leaks, it doesn’t matter if your ids are sequeneced or unsequenced, because all data has leaked anyway. The key leaking doesn’t seem like a realistic security issue.
  - zxexz 2y ago
    Ideally if you do this, you store the key in a separate schema with proper roles so that you can call encrypt() with the database role, which can't select the key. Even then, the decrypted metadata should not be particularly sensitive - and should immutably reference a point in time so you can validate against some known key revocation retroactively. My take is it's rarely necessary to have a token, that you give to an external entity, that has any embedded metadata all - 99.9% of apps aren't operating at a scale where even a million-key hashmap sitting in ram and syncing changes to disk on update would cause any performance difference.

thiht 2y ago

I don’t understand how that’s an issue. Do you have an example of a possible attack using UUIDv7 timestamp? Is there evidence of this being a real security flaw?

cqqxo4zV46cp 2y ago
I don’t understand this thinking. If you understand what’s at play, you can infer the potential security implications. What you’re advocating for is being entirely reactive instead of also being proactive.
- thiht 2y ago
  No, I don’t. Even with a timestamp uuids are not enumerable, and honestly I don’t care that the timestamp they were created at is public. Is the version of uuid used being a part of the uuid considered a leak too?
whynotmaybe 2y ago
The draft spec for uuid v7 has details about the security considerations : https://www.ietf.org/archive/id/draft-peabody-dispatch-new-uuid-format-01.html#name-security-considerations https://www.ietf.org/archive/id/draft-peabody-dispatch-new-u... The way I see it is that uuid v7 in itself is great for some use but not for all uses. You always have to remember that a v7 always carries the id's creation time as metadata with it, whether you want it or not. And if you let external users get the v7, they can get that metadata. I'm not a security expert but I know enough to know that you should only give the minimal data to a user. My only guess is that v7 being so new, attacks aren't widespread for now, and I know why the author decided not to focus on "if UUID is the right format for a key", because the answer is no 99% of the time.
- thiht 2y ago
  That just seems overly cautious. I’d rather use UUIDv7 unless I have a reason not to. The convenience of sortable ids and increased index locality are very much worth the security issues associated with UUIDv7. Maybe I wouldn’t use UUIDv7 for tokens or stuff like that, but DB IDs seem pretty safe.