RSA: finding e given n, m and c So I'm not sure if this is possible but assume I have 

$$c \equiv m^e \pmod n$$

I have $c$, $m$ and $n$ but no $e$, which in my case I a value that can be up to 15 digits. Is there a way to do this?
As SEJPM suggested, it's quite practical for the range of $e$ in question.

Here's an easier way than the Kangaroo method:


Set $\lambda \approx. 10^{7.5}$; the exact value isn't important, but the below works most efficiently if the approximation is close.
Compute $A_i = c m^i \bmod n$ for $i = 0 .. \lambda - 1$ using about $ \lambda$ modular multiplies
Store all the $A_i$ values in a fast lookup table (e.g. a hash table)
Compute $z = m^\lambda \bmod n$ 
For $j = 1 .. 10^{15} /\lambda$ compute $B_j = z^j \bmod n$, and check if the value $B_j$ appears anywhere in the $A_i$ list.


If we have $B_j = A_i$, then we know that $e = \lambda j - i$

Assuming $e$ is in the range $0 .. 10^{15}$, this will always find it, using about $2 \lambda$ modular multiplies; quite doable on a standard PC.