1. | concept
Number of blocks found since the block a specific transaction was included in
2. | security
Each block has a set of transactions included in it, which build off of previous transactions. For each block after the block a transaction is included in, the more secure that transaction becomes.
3. | information
Due to differences in implementation, different coins require different amounts of confirmations to be sufficiently secure.
Since each confirmation adds another level of security, it's important to use the appropriate level of confirmations depending on the blockchain, and value of transaction
3.1 > Ex. | Bitcoin (BTC) small amounts
RBF (replace by fee) is a feature of Bitcoin (BTC) which makes it simple to replace a transaction before it has a confirmation and send it to someone else. Once a confirmation happens however, it is incredibly hard to reverse.
Even if the transaction does not have the RBF feature enabled, it the miner fee is too low the transaction can get stuck in the mempool for multiple weeks and eventually removed, effectively reversing the transaction.
As such, we recommended waiting at least 1 confirmation for all BTC transactions.
3.2 > Ex. | Bitcoin Cash (BCH) small amounts
Once a Bitcoin Cash (BCH) transaction is broadcast to the network, any further transactions attempting to spend those coins again will be rejected. Since the Bitcoin Cash (BCH) blocksize is sufficiently large, every transaction will be included within a few blocks.
Bitcoin Cash (BCH) does not have RBF, which makes it much harder to double-spend a transaction. As such, as soon as the transaction is broadcast, BCH low to medium value transactions are sufficiently secure.
3.3 > Ex. | Bitcoin (BTC) large amounts
6 confirmations is the standard for effectively 100% irreversible transactions. Typically 2-3 confirmations are enough, and 6 is very cautious.
3.4 > Ex. | Bitcoin Cash (BCH) large amounts
6 confirmations is the standard for 100% irreversible transactions. Typically 2-3 confirmations are enough, and 6 is very cautious. Since BCH has a minority hash power, if the amount being sent is large I would recommend waiting for an additional confirmation over BTC
* All terms and definitions may change as the Cryptionary improves